This is the way I saw relative play (so, how well you did compared to how good your start position was):
S Tier - almost perfect play
1. Naples/Fitz/Colkate - Essentially flawless. Negotiated the Italian problem relatively well, destroyed a Lucky Nation Ottoman Empire (even if this was pre-patch), has managed to set up a relatively safe area of expansion into the Middle East, compared to most other European nations which are now locked off, etc. Basically no flaws.
2. Viyajanagar/Toma - Basically the same as above in terms of almost no problems with play, just in the context of not really having the same competition, especially now Ming is gone. If the Westernization goes fully successfully, definitely pushing Fitz for the top spot.
A Tier - excellent play
3. Sardinia-Piedmont/Savoy/Morfeo - Savoy has a really nice start, probably the best of the Italian nations, but even so Morfeo's done a fantastic job with it. A missed chance with colonization, I feel - with Spain relatively inactive and (at that point) an uncontested West African coast (Morocco would be easily enough deterred with Western troops) meant a missed chance to hit a relatively empty America. Very few problems, only a gap between Morfeo and Fitz/toma because the latter both have set up clear paths of expansion whereas Morfeo has boxed himself in, perhaps unnecessarily.
4. Venice/Archenemesis - a harder start than Savoy, admittedly, but played nearly as well. Even more boxed in than Savoy, though, which is the major reason for losing out. Admittedly, could expand relatively easily into Austria, but I'm less convinced than some this would be a good idea. Austria currently acts as a lodestone to Italian politics. If Austria falls and Venice and Sardinia-Piedmont both start expanding upwards, it's very rapidly going to upset the tenuous balance of power in Italy which has allowed the Italian nations to do so well in the first place.
5. Japan/Hosokawa/Mgo - While like Fitz, Mgo benefited from pre-patch mechanics a little (Japan's now a somewhat nastier environment), excellent play. Somewhat frustrated by Kabouter while he was there, but that gap is now wide open. Could perhaps have pressed his advantage a little more against Ming in the last war.
B Tier - good play
6. Hedjaz/Sickboy - Hedjaz has done well in uniting the Arabian peninsula, that's no mean accomplishment. However, that position has been exploited perhaps to full extent - Africa (and colonization in general) really hasn't been particularly competitive this game. There was definitely more room for expansion and resultant trade monopolization.
7. Ming/Kabouter - Kabouter was doing really well, but quit.
8. Morocco/Mleuigi - Benefiting very much from the fact that the European powers are either occupied or not fully utilizing their strength (particularly Castile/Spain). Having said that, has definitely made hay while the sun shines, with the rapid colonization of Brazil. Definitely should be looking more towards gearing Morocco up for a greater role in the Mediterranean, though - while expansion has been good now, it might get tricky if Spain or Sardinia-Piedmont decide to use Morocco as a potential route of expansion.
9. Novgorod/Crab - Generally speaking has planned out a strategy that works well, but, when things depart from the plan, makes rash decisions. Given that, has done reasonably well - particularly the annexation of Pskov from under Muscowy's nose and the vassalization of Norway leading to America, but impatience has caused a lot of troubles, particularly in the religious sphere that has wasted some potential progress. Hasn't set up a particularly good expansion plan, though, which is going to prove damaging.
C Tier - reasonable play
10. Scotland/Mali/Rug Monkey - Made good gains as Scotland, got ruined by AI, was unable to secure his advantage. A better safety plan such as greater Irish holdings might have helped Rug's position, but it's difficult to say. Did little as Mali.
11. Poland/Manik/Cazz - Has definitely made gains, but not really the gains you'd expect - i.e., Sweden and not Lithuania, Crimean territory but not Wallachia. The losses are all regain-able, given Lithuania has the same dynasty and Moldovia should be relatively weak, so not really losses in the true sense of the word, but definitely delays to growth. Probably the main problem is the MIL tech in comparison to the neighbours - much like fanboi below, the wealth and manpower is there but the troops aren't there to back it. In a good position at the moment, though - winning the war with Lithuania, making a lot of money thanks to Protestantism and wealthy German provinces near Brandenburg, and in a position to claim lots of territory in the near future.
12. Burgundy/Fanboi - Hasn't really shown the growth you might expect, probably due to early over-aggression leading to poor teching. Appears (?) to have the money, given the trade node control and potential for cheap mercenaries, but that's not much use when your army is shit. Given the current state of the Holy Roman Empire, definitely could have expanded more that way.
13. Spain/Castille/Face/Sir Digby - Probably under-performed compared to AI Castile, but then is new, so that's not terrible. Basically did what Castile does (i.e., form Spain laughably easily thanks to the Iberian Marriage event), but should have more colonial presence and not have kept losing stuff to Grenada. Showing progress.
EDIT: Discovered this was in fact due to AI ineptitude. My deepest sympathies.
D Tier - poor play
14. Denmark/Sweden/Georgia/Wink - Sweden shouldn't lose that badly to Denmark, that was really catastrophic. Then, given the much larger Denmark resulting, hasn't done much with it, although admittedly is facing a large number of loans and so on to deal with. The fact Lubeck isn't under Danish control yet is puzzling, given how much having control of Lubeck means for finances.
15. Austria/Wallachia/KingSnake - Poor Austria.