core i3 2100 offers larger upgrade path, wider motherboard and chipset choices.
3850 offers strong igp performance, narrower motherboard and chipset choice. upgrade path seems to be locked so far. rumor is, amd will replace socket fm1 (3850's socket) with socket fm2 for future apus in 3850's class. then again, amd is known for backwards compatibility, so you never know.
this becomes easier with your gfx card choice. imo, the core i3 will be able to provide decent cpu performance with your gtx 550ti. if you can hold out till april/may you could even try getting ivy bridge after they launch and get reviewed.