Unless you're going to be taking it everywhere, the iMac is probably a better choice.
The iMac has the IPS screen, as you mentioned.
Quad core i5 2.5Ghz CPU
512MB 6750 Discrete GPU
4GB RAM to start.
Mini
Dual core, (likely) 2.3Ghz i5 - 2.7 i5 CPU
Integrated Intel HD3000 256-348MB shared system RAM (which are being slated on this forum at the moment, although if you don't game, maybe irrelevant)
2GB RAM to start.
Fair bit cheaper.
However, factor in the monitor cost, the mouse and the keyboard and you might not end up far off the cost of the base iMac, which, if nothing else, will look a hell of a lot nicer than a Dell monitor with wires hanging out all over the place. Maybe that's just my inner neat-freak talking.
Both are crap from an upgrading perspective.
For me, it'd be the iMac every time.