I've only heard of a few cases of bitcoin-mining trojans... most notoriously by a game company (E-sports) where the company ended up having to pay back way more in restitution than they allegedly made. They only made about $3600 (according to the article below), and was ordered to pay back over $1 Million USD. There are others in the wild, but that's the one that's been in the news lately - and that's one of the only ones we have figures for how much was made by the infections. You can read about the incident here:
http://arstechnica.com/tech-policy/...les-covert-bitcoin-mining-case-for-1-million/
Ransomware seems to get way more coverage, probably because of how intrusive/destructive it is for the end user... but since we don't have figures on how much the other ones have made (that I know of), it's hard to really compare the two in terms of how much money was invested/made/lost by the criminals.
Either way, don't write anything like that!