DSI has more horsepower than a DS Lite
The DS Lite Cpu is 66MHZ , while the DSI Cpu is clocked at 133MHZ .
The DSI Has 15MB of ram , while the ds lite has 8-4 mb of ram
A NDS Game won't look better on the DSI because its made for the DS . But a game special for the DSI will look much better . A NDS game has a limit from 256MB , a DSI game could easy be 512MB .
So don't buy a DS Lite hehe .
I would get an DSI , the dsi LL has some bigger screens and bigger pixels so game wil look much more blocy than on an DSI . Also the DSI is cheaper than a DSI LL . And the DSI LL looks hard to put him in a pocket