Aside from Prussia
Sweden: Very good literacy ,good position for early industrializing and fast technological progress (not to much pops) ,Scandinavian events come somewhart early but you can gain a lot there an make Sweden powerfull.
Spain: Somewhat annoying early events ,but youre in a very secure position and Spain ,although somewhat larger to industrialize ,has quite some potential later on.
Portugal: Smaller ,but in a good spot for colonization ,easy to industrialize
Belgium: War at first but after that easy ,although somewhat uninterresting posiition ,very good technological position
Netherlands: Somewhat similar to Belgium ,but somewhat worse industry at start ,good colonies though.
Switzerland: Easy to industrialize ,but limited potential and not very interresting position neither.
Brazil: Larger ,but not to much pops in much state's ,takes some time to industrilize and gain on the Europeans in tech ,after that immigration can gain you a lot.
United states of America: Some tricky events ,but large and quite wealthy ,can become a massive superpower
Urugay: Small ,but can get loads of immigrants ,and tech should be fairly fast.
Intermediate:
United kingdom: very large ,easy to industrialize but also lots to invest to and to keep you occupied
France: Large ,fairly good early position but takes quite some time to industrialize ,moderate tech position ,lots of events and some political problems.Once industrialized can be very powerfull ,Algeria is also a plus.
Italian minor's as Sardinie Piedmonte ,papal state's and 2 sicily's ,Italian unification is somewhat of a challenge ,but once achieved italyhas quite some potential.Because most minor's industrialize fairly quick on themself you unify a fairly industrialized country.
Austria: About the same as france ,large ,takes time to industrialize ,some bad events and has to fight of some country's ,but once industrialized quite powerfull.
China: Uncivilized ,and gets to fight of the brits to ,but it's very rich so a for a human not that hard ,Very large so takes a lot of time to industrialize and technoligy will come slow.
Japan: Uncivilized ,but gets civilized by event and gets a good tech position mid game ,medium sized so industriazing is pretty fast ,Is quite rich by norm ,gets to be bad boy in Asia.
Greece: Somewhat backward and small ,innitial position is not easy to overcome especially if Turkey is strong ,but once cores are reached a fairly good country ,hard to become a major though.
Other minor's of Germany: Like Bavaria or hanover ,can be fairly strong early on ,but lots of fights before Germany is yours.
Most other South American country's ,Somwhat lesser technological start ,no industry's usually ,takes longer time to industrialize and fairly uninterresting position.
Transvaal: Good technological start position ,can get wealthy with precious metals early on ,can get big lumps of Africa but UK is a danger.
Hard:
Krakow: Can become Poland ,but small ,very good tech spot ,can get many immigrants ,not to few manpower neither ,but surrounded by big boys.
Ottoman empire: Some hard events here ,and not an easy country to industrialize ,but in a good position for GP to the end.
Mexico: Large country ,but with lots of problems ,and not that rich
Persia: Uncivilized ,can get civilized by event but prepare youreself for bloodshed ,especially if Russia is in it's bad mood.Once industrialzed though it becomes powerfull in Asia ,but has a lot of big boys around it.
Serbia: Small ,but lots of cores ,has to fight of major's though to reach full potential ,then can be a large power in Balkan.
Egypt: Uncivilized ,but not to small ,still quite a challenge.
Indian minor's: Surrounded by Brits ,hard to get civilized ,but fairly wealthy
Siam: Fairly wealthy ,epecially with precious metals ,but not to easy to civilize
Very hard:
Most uncivilized country's ,especially the smaller ones.
Sattlelite's like Ionian islands
Well thats about it i guess ,add if you wish