DS games generally look sharper and crisper on the DS Lite. There are two options of playing DS games on the 3DS/3DS XL.
The first is to have the DS game scale to the full size of the bottom screen on the 3DS, which results in a blurry mess, as the games are blown up to fill the screen, but not at a good ratio. Text looks like garbage, and as does most sprite-based games.
On the other hand, you can play the games at their original resolution. This makes the DS games seem extremely crisp on the 3DS, while DS games on the 3DS XL look about DS Lite sized, give or take. This is probably the best way to play DS games on a 3DS, if you can stand the empty space on the sides of each screen.
I haven't had a chance to properly play DS games on a 3DS XL, but I haven't experienced any of the "yellow tint" that others seem to have with their 3DS/3DS XLs, so I guess I got lucky with my 3DS. I've found that my favorite experience playing DS games was on a DSi XL, with the DS Lite coming in second. My verdict is that if you have access to a DSi XL or DS Lite, try to keep your DS games on there instead. While backwards-compatibility is a great feature for the 3DS line, it just can't match up to hardware designed with the DS's games in mind.
DSi or the even better DSiXL is the best for DS games.
The 3DSXL is okay and the DS Lite IMHO is not better than the 3DSXL. If anything, the DS Lite is only better than the classic DS, in terms of how DS games look, IMHO.
I haven't notice any yellowish tint (however there's a blueish tint in Power saving mode) on the XL. I've only truly noticed screen stretching while playing the Pokemon main series but even then holding start or select while starting a DS game sets the game to it's standard screensize (which is noticeably small on the XL). --- I love Nowi!!! http://tinyurl.com/a8cjh32 3DSXL FC: 4640-0379-8455 PSN (PS3+Vita): TehTrumpCard
It looks far better then the 3DS but it looks worse then the lite.
DSiXLs look by far the best with DS games they look sharp they stretch it nicely and looks crisp and freaking beautiful.
DSis look decent and dont really stretch much it looks better for the off game but genrally not as punchy as the iXL.
the Lite looks worse then the two above but looks alright.
the 3DSXL looks uglyier and blurrier then the lite but it has far more colour contrast/less darkened image then the 3DS
the 3DS looks like a steam pile of ass with DS games where the text is blurry and looks like a pile of crap. the resolution in full mode looks horrendous out side of select games (mainly 3D models like SM64DS ACWW or metriod prime hunters) but sprite games like pokemon or megaman ZX looked butchered. --- ErrorSupply 3-D DS -OMG! It's the ultimate anti-pirate tech O:.