Among the three - I551 gets my vote,
but in similar budget, better phone would be LG Optimus One, and for looks you can check out HTC wildfire.. I think it has good design, though the screen is supposed to have too less pixels for proper Android experience.
X8.. I dont think is a guy's phone NOM
My team mate has a pink one, and it actually looks really good with her. So, if you're a girl, u can definitely opt for that one
(and update the Android version to 2.1 if you like).