mining doesn't cost me more than running my computers already does.
Mining will cost more than having a PC sit idle, always. If you're mining, the CPU or GPU is FULLY utilized and will typically require MUCH more electricity to use than if it were doing nothing or just running a screen saver. Plus there will be significant cooling required, so whatever fans the PC has will likely be going full speed.
Yes, but my PC's never sit idle. If I weren't mining, I'd be running BOINC, or 10s of VMs. So its not much different, since BOINC would be eating all my cores if mining wasn't.
Good point. Then there is really no downside. You have no investment cost and no increase in operating costs.
ASICs have hit scrypt, so consider mining scrypt-n (vertcoin) or something else that is equally ASIC resistant. Get a couple good mind-range GPUs like R9 270. The 270 is about $200 and will do 225khs on scrypt-n (450khs on script).
Nothing is good for CPUs right now. If you have free credit, just mine the same thing as your GPUs are mining, or maybe target a newer coin with very low difficulty. Check out whatmine.com. There are profitable coins listed with a difficulty below 1. Sounds like a good place to target a CPU.
If lower difficulty equals better return, protoshare should be very good, right? Difficulty: 0.036228