(I have a DSi XL)
I personally love the big screen. Although the same screen resolution, it looks better.

Screen resolution isn't a huge deal unless there's teeny tiny text to read (when it scales-up it can be harder to read). One thing that many don't realise is some games are actually capable of running at a higher resolution so they actually take advantage of the bigger screen size.

Definitely less portable though; I think that would be a bigger factor in your decision.

One thing that many don't realise is some games are actually capable of running at a higher resolution

not true at all. the big XL screen has exactly the same resolution as all the other DS models... 256 by 192 pixels

Even my wife can carry her own DSi XL around with no problems at all. Is it as much portable as the normal DSi is. We're talking just a few gr and cm more, people...
As for the screens, well, there's no comparison. The DSi XL screens provide excellent, vibrant colours from all viewing angles, i.e. there's no shading and loss of colour depth when viewed from odd angles as is the case with the standard DSi.
It's just a totally different (and better) experience.
DSi XL all the way, yeah!

I didn't say the screens were higher resolution I said the games could run at higher resolution. Technically the XL has the same resolution as a regular DS/DSi, but if the developers used more detail in the graphics than necessary it doesn't look "blown-up" on the XL. Some developers create less-detailed artwork because they don't feel a need to do more as they're limited by the resolution of the DSi, and the result is that with proportionally larger pixels it does have a bit of a zoomed-in feel to it. This is most notable with text graphics like the characters on mahjong tiles; for your typical action/puzzle game you won't notice.

I have also purchased Nintendo DS XL and it is one of the most efficient Gaming console by Nintendo. The screen is also impressive and cool unlike the other people said about it.

DSi XL is too big and ugly.
Never got one, never wanted to.
I have a DSi, hardly ever used it, R button broke quickly, was a complete waste of money.
Get a DS Lite, it beats them all.
Just gotta sacrifice DSiWare, but oh well.

The Xl is the best way to play DS games.

I have had both Dsi and DSXL and the 3ds.

I liked the DSXL and think it should be the default ds size. But with a sharper resolution.

Having said that I have traded my XL in now for the 3ds and when playing ds games I don't miss the big screen.

I play most of my video games at home, so portability really isn't an issue for me. DSi XL, for the win.

I got 20 out of it. LOL.

The only difference between it and XL, the size, design and it has better speaker power oddly.

I prefer the DSiXL over the DSi. It has better battery life, nice screens, and is a lot more comfortable in the hand.