Desktop and I suggest (1) not to overbuy and (2) spend more on the display.
An 3rd gen i3 is more than adequate for most users, unless you have a deal that you can't pass.
In addition to my clone 2008, I bought an Acer i3-2120 in 2011 and it feels great. I added a video card, it was cheap and the w7 64-bit license was included.
A Dell Inspiron 660 i3 or i5 is a great deal these days. I would add a video card HD6670 for 65$ and be done.
For whatever reason, I don't feel that my computer with an Intel SSD is significantly quicker and I would stick with a 7200rpm HDD.
2007 E90 AW 323i Step | Lowered 1.25"/1" | BMW Performance Exhaust | Debadged | Scangauge II | Style 162 18" & 161 17" wheels & rear 15mm spacers