[[ I've been debating between a 27" iMac or a Mini with a 27" Thunderbolt display. ]]
Even if you decide on the Mini, DON'T buy the existing thunderbolt display.
It's out-of-date, overdue for replacement, and the price is far too high compared to other displays of equal quality.
For years I was a "tower" guy, my last one being a PowerMac g4 MDD. But I picked up a white 24" Intel iMac back in 2007, and liked that, too. Almost made me "an iMac guy".
But after 9 years, the g4 needed to be replaced. The new 27" "thin iMacs" looked nice, but I didn't like the idea that it was difficult to get into them, and I'd read enough reports of screen problems to make me unsure about that.
So... I bought the 2.6ghz Mini, and have been satisfied with that. Quite a nice "jump up" for my "main" computer, after the g4.
That was my decision, you have to make your own.
The new iMacs certainly look attractive, but they'll cost you a good deal more.
Be aware that the release date for a new 2014 Mini could be drawing near. Could be as early as the end of the month, but no one can say for certain. It will probably still have "built-in" graphics (no dedicated GPU), but they should be MUCH improved. Aside: I have no complaints at all about the graphics on my late 2012 Mini -- but then, I'm not a gamer, no interest in that whatsoever...