In 2011 I built my own desktop with a 2nd gen i5, 16GB RAM, an MSI nighthawk twin frozr GPU, 6 TB storage (2 HDD, 1 SSD), and a nice amount of fans/heatsinks. It was more than 2x cheaper than buying a prebuilt one (low thousand).

Last year I spent $400 to upgrade the motherboard, got a 5th gen i7, 32GB RAM, a GTX 950, and 6 more TB of storage (2 HDD and 1 SSD). Yay Newegg and microcenter sales!

I've never had an issue with any of the hardware, my build times are miniscule (MBP chokes on some of the stuff I compile), and I could have 10+ projects open in Android Studio / Intellij, 20 tabs in chrome, a terminal emulator, docker, and Plex, and it doesn't break a sweat.

If you don't need to be mobile that often, I'd definitely go desktop.