I started with ME1 and ME2 on xbox, since my PC wasn't good enough to handle them on there. I played about 8 or so characters thoroughly on both games for xbox. Then I got a good PC, bought and played them on there.
I think I will definitely go just PC for ME3. I might not get all those save games from my 360, but I have remade half of them on PC already and am fine with playing it more to get the rest if I ever wish to do that. It's not even much of a problem with the advantages of PC versus console, but I hardly ever play xbox anymore and my PC is actually easier to use now than my xbox is to setup and all. So PC wins in all departments for me.