My kid sister only had Playstation consoles before we bought her a 360 together with the great game Kameo (cute and very Nintendo-like). Other than Kameo and Tomb Raider there weren't many games which interested her, so the console didn't interest her anymore and it RRoDed on me after playing Gears of War (wasn't as good as I expected) or due a firmware update and we sold it soon afterwards, this also due to bad support. She now got a Nintendo Wii and loves it!
Personally I didn't own a home console (me and my girlfriend do have 2 NDS Lites) since the Nintendo 64 (I loved Mario 64 and bought it at launch, but no other N64 game came close for me). Once I have a beefy PS3 games library my sister will get a slimline PS3 so she can play games like Ratchet & Clank, Jak & Daxter and Singstar on my partent's big screen HDTV.