The Venom is pretty programmable (in the computer, or even from the panel) and can do quite a bit if you are creative. Also has 3x the voice count and run four patches at once. Get it on sale, Amazon sometimes has it for under $200... I bought mine when it was $167... Of course, these have been discontinued so don't expect any updates.
Microkorg is not all that flexible, has minikeys, and is quite a bit more expensive.
I feel the Venom is a better deal all around. More voices - less voice drop for long ambient pads, full keys, cheaper price, many years newer design (guy that help on the Andromeda was part of Venom creation). Microkorg is good basic, decent snyth, but... less voices, more expensive, tiny/less keys, more one trick than the Venom - which is 2 or 3 trick.
I own a Venom and have played around with the MicroKorg numerous times. It really is somewhat unfair to give a complete review of a synth you don't own but I can't stand the MicroKorg. It has a completely unplayable keybed to me. The Venom's is not good but you can definitely play it without cringing as badly.
As far as sound creation, the Venom is actually really good if you update the firmware and use the latest editor. Forget about editing from the front panel. You can't even get to half the parameters that way. Support is absolutely and completely non-existent for either the editor or the synth though now. The forums used to be pretty active. I was a beta tester of the firmware and the editor for the Venom. To me, the biggest gaping hole in the editor is that the arpeggiator editing never happened. The Venom has a lot of built in arp patterns but you need to open the control pattern and drop midi files in to create your own. That just sucks. They had promised a VST version of the editor which also never happened.