Depending on how aggressive your current knobbies are, you be very to extremely happy with street slicks.
When I got my bike (used), it had Panaracer Smoke's on both wheels (look that one up) I was pedalling my butt off to get any speed. Quit pedaling and I'd coast about 20 yards and nearly be stopped!
I weigh about 230 and have found a 26x1.50" to be about right for my needs. It's "fat" enough to kill road buzz and rolls pretty decently. IF I didn't have so much rough textured pavement, I'd probably go for 26x1.25".
I'm using Serfas Drifters. I havn't used any other brands in that size, so I can't give any comparison, but they seem to do the job and other Drifter owners seem to feel the same way.
BTW, use proper tire sizing. For example, a 26x1.50" IS NOT the same as a 26x1-1/2"! Decimals and fractional sizes are not the same.