Computer, absolutely! For all the above reasons.

Cadence is also very important to me. The dbl4w computer I have (23$ at MEC.ca for the canadian folks, but I'm sure you can find them in the US somewhere) has cadence, so that's proof that's you don't need to pay big money for that. I use it to self-monitor myself: sometimes I don't realize that I'm tiring myself out but I check my cadence monitor and realize I'm at 70 rpm. Time to get on a lighter gear. I instantly get better...