What area of Menlo Park? I'm a Bay Area resident since 2005, and was in the Palo Alto area for 5 years (4 attending Stanford). Down by Sand Hill, etc, is really nice but more expensive. Up by 101 is cheaper, but neighborhood not so great. It's got a nice downtown and with the closeness to Palo Alto, Mountain View, etc means that there is more tech-y stuff going around which I like personally, but not sure where your interests lie.
I'm not too familiar with San Carlos though, so can't compare.