South Nashua is pretty Nice, so is the Broad st area out towards Hollis. North end by Greeley street is my personal favorite though. Lovely homes on tree lined streets, queit and nice but still walking distance to downtown.

Truthfully with the exception of tree streets, parts of downtown, and possibly French Hill, everywhere in the city ranges from decent to nice. French Hill is a bit crappy but overall not bad, just kinda dumpy.

Edit: I also forgot to mention the Fifield street area, south east of downtown. Again, quiet and nice, homes are cute and nice, but still walking distance to downtown.