i confirmed about s advance from various sources like team-bhp(mobile thread), this site and other reviews on flipkart and i even read that this phone is soon to be discontinued.
I am in same boat as yours.....just now i have also included XPeria U, it does not have expandable meory but i am judging my memory needs. i guess 4 gb should be fine for me...right now i have a bb 8520 with 2 gb memory card and i hardly used even 50% of that....so if my memory needs settles under 4 gb available on xperia u then xperia u is the best bet as it has removable battery and front camera at less price then both one v/sola. Sola misses on front cam while one v don't have dual core. you can see no phone is perfect so we have to analyze our priorities and then make a decision.