Own both and I've spent more time playing and enjoying the MS indie titles (Powerstar Golf, Max, Peggle2) than the free offerings of PS+ (Outlast, Dead Nation, Contrast, Warframe). I did enjoy the short experience of Flower. But that's just me and my opinion, looking at it from a purely gaming standpoint it's easy to argue that Sony has offered more indie titles and more free ones.
Something about the free ones for me is that since I didn't pay for them I don't feel like I "have" to play them. For example in Outlast I got stuck and after 20 tries just gave up. Now if I had invested in that title I may have put more time in and got through it and be able to put that experience up there with the MS indies I've paid for and conquered.
That said, most of my gaming time on the new consoles hasn't even been about indies, it's been about the blockbusters and thus far MS is way ahead for exclusive experiences. The gap narrows somewhat with Infamous but I'd still give the overall edge there to MS. As for multiplats, Sony gets the slight nod as I haven't really seen any mind-blowing differences between the 2 but won't argue the comparisons saying Sony wins.
So just from a gaming standpoint, Sony and MS are about equal. MS has some neat stuff going on with the Kinect commands and snapping while Sony has offered up some pretty entertaining latenight "Live from Playstation" amateur events.