What is your budget? Huge difference in areas.
I'd steer clear of Stoke Village. I think years ago it used to be a nice area hence the big Victoria houses but it's not great now and near the actual village itself it's a bit rough. A lot of those lovely big houses have been converted into flats as well.
Mannamead is nice. One of the more expensive areas. I'd love to live there but budget wouldn't allow. Eggbuckland is quite nice as is Crownhill. Plymstock is very nice and Plympton. Hartley and a lot of Manadon is nice. These are all the more expensive areas.
I'd avoid Barne Barton for definite! Personally I wouldn't live in Devonport although I know they are trying to do it up, I still wouldn't go there, same with North Prospect (more commonly known as Swilly). Greenbank and Mutley are studentville, I'd avoid them. St Judes is nice but you are only ever likely to get a courtyard, not a garden. Lovely houses though. Derriford and the Looseleigh Lane areas are very nice, as is Roborough and Woolwell.
It completely depends on you budget though. You'd need a good budget of at least 170k to get a nice house in one of these areas. You could get slightly cheaper but there would be something about it that was making it a lower price.
Also avoid Ernesettle, Honicknowle, St Budeaux (although Higher St Budeaux is lovely, it's further down the hill near the square you want to avoid), a lot of West Park, some of Whitleigh although some is okay, bit street dependant that one. Avoid some of Ham, again a bit street dependant. Kings Tamerton is fine as is Beacon Park, that's quite nice. Southway is a bit hit and miss again.
So some are lovely areas but expensive, some avoid like the plague and others are ok depending which part you are in.