ntbrite, the model would depend on your needs.
I would pick a model with an intel processor though (basically anything that's been released in the past 4 years would do).
Desktop? Mac Mini would probably be a safe bet (if you have a display, keyboard, mouse etc you could use with it) and it's the least expensive.
For all in one desktop, iMac wouldn't be bad either. Those are also very easy to sell again after you'll upgrade later (basically all Macs are).
Portable? MacBook for more portability and cheaper price, or MacBook Pro for more screen and fancier features. Of the laptops I'd probably start with MacBook though.
Mac Mini is actually very mini as a desktop. I've flown a few times with a Mac Mini in the hand luggage in a plane - when I had my laptop(s) in the same luggage.
So you could also use in multiple locations - as long as you have all the other accessories in the other location too (home/work for instance).