I was thinking of getting one of them but I have a few questions.

1. Which one is the best?
2. How difficult are they?
3. How good is the replay value?

Any help would be much appreciated.

III - Dracula's Curse (NES) -- by far the best available if you ask me. All of the available entries in the series have high difficulty, but it comes in somewhat different forms; II - Simon's Quest has a different kind of difficulty from the others, based sometimes on obscure puzzles or just having to find the right wall to break in order to proceed. III has difficulty based on the fighting and platforming, which is quite varied across the course of the game's many levels.

I'd also say that III has by far the best replay value, since the levels are structured into branching paths, where each journey through the game will take you through different sets of levels, and you'll encounter different "helper" characters as well based on the paths you choose. These helper characters have completely different abilities from the main character (Trevor Belmont), and once you meet one and let them join you, you'll be able to switch back and forth between Trevor and your helper at any moment.

What about IV? I've heard it's different from the others but I'm not sure what that means.

You could start with IV since it's essentially a retelling of the first one but if this is your first go around with Castlevania, I think it will be hard to go back and play III which I feel is an essential play through for any Castlevania fan.

Anyways, as far as difficulty goes, I think at first most of them are extremely difficult with a decent learning curve, but once you get a feel for the series, they all have a very adaptable difficulty....still after all these years, i still hate the medusa heads.

Yeah, for some reason I've never particularly cared for IV... but now that it's come up in this conversation, I'm thinking I might download it and play through again for the first time many years, see how I like it now. I believe it just originally disappointed me in its music, atmosphere, etc insofar as Dracula's Curse did all of those things much better, in my mind.

Super Castlevania IV rulez so hard...highly rec'd. its a good one to start on cause its not as brutal as I,II, or III. you cant really screw up though, its all videogame dope.

IV is the most polished and I love being able to swing with the whip.

III is the hardest and perhaps the most critically acclaimed.

II is the unique one, but I think reapparing on the same screen when you die makes it the easiest.

I is my favorite and is a great pick up and play adventure. The length of the game is perfect.

Super Castlevania IV imo.

1 can be very unfair at times. Many cheap deaths.

3 is hard but I can at least progress through it more than the first one.

Rondo is the hardest of them all. Even a regular Axe Knight gives me problems.

Rondo of Blood for me.

It's fairly difficult, but if you take your time it can be really fun.

There really isn't much replayability, but there are branching pathways, and you can choose whichever level you've unlocked and play it however many times you want to unlock another pathway.

Most people I know say IV is the best but I've only played 1-3. 3 is better than 1 and FAR better than 2.

I'll toss some more love behind IV. It's very difficult, but only rarely does it seem unfair. (Well, comparatively rarely...those NES ones are downright brutal!) But the music is awesome, the graphics and stage effects are phenomenal, and it's a lot of fun. Definitely one of my favorite anythings on the VC.

Super Castlevania IV.

Super Castlevania IV is my favorite. Ronda is alot of fun but is possably the easiest platformer iv ever played. Also Castlevania Rebirth on WW is damn good.

I'm sure this guy is thrilled for all these answers... over a year after he made this thread...

Castlevania III: Dracula's Curse. I can't beat it, but it's the best.

Haha, fair enough! But hopefully others can benefit from these replies as well.

On a related note, which would you guys say is the best Castlevania DS game? I'm playing Symphony of the Night for the first time and loving it, and from what I understand, the DS games follow the template for exploration established in that game. Which would you recommend?

Akumajou Dracula X Chi no Rondo is the best Castlevania game available on the VC, imo. I honestly don't find it as hard as others claim it to be: I think the difficulty is medium-based at best. I find it best to go at a steady pace and follow the enemy patterns (just like I do with Super Ghouls'n Ghosts, but never mind that). The anime cutscenes are really fun to watch, and the soundtrack rocks. I also find it fun to control as either Richter or Maria.
EDIT: Another thing I like about this game more than the other traditional games is that you don't immediately die when touching spikes (thank goodness), and you only get to experience the "Ninja Gaiden Syndrome" while in the air (whilst in the past games the only place you could not be pushed back from enemies is while you're on the stairs).
_{I even reviewed this game earlier this month, link's in my signature}

@Chicken

I heard Dawn of Sorrow is the best but I havent played that one. Order of Escalia I liked more then Portrait of Ruin but I thought both were good.

I can no longer recommend the GBA Castlevania games. Compared to the DS games, they now feel very poor in comparison. Plus I feel like two screens is perfect for these style of games; its very handy to see the map, your stats and other things while playing the game instead of stopping and switching to a sub-menu. I love all the DS Castlevania games.

Castlevania 3

You're gonna get a million different answers, man.
Castlevania 1 for the NES is the most classic, and I prefer it the most. However, it's also the most basic.
Castlevania 2 for the NES is the least linear, but it's also the easiest and most rough around the edges.
Castlevania 3 for the NES is the most advanced of the NES games with the most features and gameplay options that greatly extended replayability and made things easier for both the inexperienced and the patient. It is, however, the most frustrating, with some downright evil level designs and bullcrap moments that'll leave even the most hardcore of gamers fuming at the mouth.
Super Castlevania 4 for the SNES changes things up with a new gameplay style, and it's most technically advanced of the VC CVs. However, it also goes back to the level structure of the first CV, removing a lot of the gameplay features Castlevania III set in, which gives it far less replay value. It's also kind of on the easy side, and it's also a Black sheep in the series. I personally don't care for it, but then again, I'm a purist when it comes to CV.
Castlevania: Rondo of Blood for the TG-CD is a return to form for the series, bringing back the gameplay elements from Castlevania 3 while still keeping the difficulty below controller-breaking levels. The Music and graphics aren't as good as Super CV4's, but it's still pretty impressive at times, and the level design is very good, and it expands on the gameplay set by CV3 instead of taking it away. Still, if you liked the gameplay in Super CV4, you'll be frustrated by the less lenient control scheme in Rond of Blood (which is similar to the rest of the series).

If you're looking for a game to start you off with the series, I highly recommend Castlevania 1, because if you like it, you'll like the rest of the series, since they all build upon its foundation. If you're looking for an easier and more unique game in the series, I'd recommend Super Castlevania 4, since it's the most visually impressive and the gameplay is very different from the rest of the series. If you just want the best in the series, personally I'd say that's Castlevania: Rondo of Blood. It's the culmination of the series, expanding on the gameplay, with the best balance of difficulty, high replayability, some impressive graphics and sound, and some of the best level designs and boss fights out of all of the VC CVs.