Lots of good suggestions, but just wanted to say that I live in Melrose and I like it very much. I live right near the downtown, which is lovely, dense, walk-able. The town has a friendly vibe.
Downtown is a mile and a half north of the Oak Grove T stop (orange line) and we have 3-4 bus lines down to Oak Grove from Melrose. We also have 3 commuter rail stops which go into North Station.
The neighborhoods here are very beautiful and there are lots of good spots for running, big trees, parks. The rent here is much lower than the nice parts of Somerville, Cambridge, and it is more accessible to downtown than areas with comparable rent in Medford.
That said if I had more $$ and didn't need to live on the north side of the city for work, I would consider JP. Lots of interesting cultural things going on down there. The rent is much higher though.
Good luck.