According to Hyrule Historia, Seasons is first. It doesn't really matter though.

Might just be that I played Links Awakening far more extensively than most games. (Got all the Seashells without any type of guide or anything). I know it was made afterwards but doing that allowed me to do a Link to The Past start to finish really easily. (I think A Link to the Past is better but I didn't enjoy it as much.)

Not sure whether I prefer Secret of Mana to ALLTP (I certainly enjoyed it more at the time).

Ouch. I just realised how much those 3 GBC titles actually cost you on the VC. I'd go with the new game...

For all three, it's still about half of the price for a new first party 3DS game, _{and in my country much less than the half.}

I would be surprised if the 3DS Zelda has even as much content as those three games.

Its not all about content though. Those three games are very similar. If you dont enjoy them that much, or would enjoy the new game much more, then theres no point in choosing them. If you get bored after the first, or even the first two games you've wasted your money.

Link's Awakening is a game I love so much, but I have to screech the brakes on my good memories when it comes to recommending it. A lot of the puzzles are pretty confusing, and it's really unclear on what you have to do next most of the time. For someone who knows what they're doing, it's a fantastic Zelda game. For first time players though, it will take some warming up to. It's also tough for first time players because to get the full bitter-sweet effect of the ending, you need the secret ending you get by beating the game without a game over. It only adds one little scene to the ending, but it drastically changes the tone from sad, to bitter-sweet. There's a reason most players today can't really get into the game, yet it still has a die-hard fanbase of those who grew up with it and know it inside and out.

Even if you do then you have only spent £15 instead of £40

Or you can play one a year for three years.

Edge says this about the new one " Nintendo’s nervousness around punishment, for fear of putting off newcomers, continues to undermine ALBW’s attempts at novelty."

I was a newcomer with Links Awakening so there is no way I want anything easier than that.

You just play them however you want whenever you want. I like to play some of one game for a while then switch and play the other game for a while then alternate until I beat both games.

How does that work for getting the true ending where you put the code in to the second ?