You can look on uesp to get stats on each mask. But for this character there are a couple that are very useful. Krosis ihas Fort Archery, Lockpicking, and Alchemy 20 pts but to beat Krosis you should have some resistance to magic/fire, as there is no place to sneak on him. Shearpoint is northeast of Whiterun in a mountain pass and is pretty easy to access.
Otar has 30 pts resist fire/forst/shock but Otar shoots some shock. It has a long dungeon crawl and enemies can be a few levels higher than you. It is Northeast of Markarth and most easily reached by going north of the farm on the left side of road out and sticking to mountain but no path at first.
Rhagot has a huge stamina boost but is a livid [censored] to get to unless you are a well put together 18th level or up to 22 or so.
The rest of them I can think of besides Volsung have some kind of magic enhancement enchantment. Volsung is handy for bartering and ocean diving but is also in a place that has Draugr Scourges regardless of you level and Volsung is hard to beat unless you do some tricksy archery and hide behind a tall rock down the hill a little ways and pop out and shoot him, or you have a lot of frost or magic resistance. I have had dual wielding characters with elemental fury kill him pretty quickly at around 13-16th level, but then again they can kill anything fast.