Lots of good discussion going on here, but you know what could really help? Some metrics! These shouldnt act as an end-all answer as they don't take adequately into account synergies between ideas, and certain ideas fall far enough out of the standard spectrum that comparing them to other ideas isn't 100% accurate, but it does give a good overall feel of some of the top NIs. So, without further ado-
-Ideas scaled from -1 (for outright bad ideas) to +3 (for good unique ideas/very over budget non-unique ideas)
-Generic average ideas worth 0, more if over budget (how much more compared to other over budget ideas of that type from different countries)
-Additional advisors/leader bonuses all +1
-Ex. Republican tradition worth +3 as a strong unique idea, trade steering worth -1
+1 for good synergy in ideas
So...let's look at Some countries!
Novgorod-6
Republican tradition is obviously the main benefit here. Defensive bonus is an average gain, but Novgorod gets a somewhat improved rate (with 20% considered normal). Full point of naval tradition is also over budget. Merchant means an extra free point. No penalties, as I actually like light ship costs. No bad NIs, but once again aside from republican tradition few outstanding ones.
Brandenburg-8
33% army morale is worth 2, as it's an average benefit at 10% but obviously way over base here. Goose step/Cantons are worth 2 and 1, once again since they're nicely over the going rate. The discipline bonus is as high as it gets, so that's worth 3. Covert relations impact is a trash idea, however, so that's a penalty. Finally, a synergistic bonus due to the overall high focus on combat.
Russia-9
+1 for 50% forcelimits-usually a weak NI, 50% is still a large benefit. +2 for Opprichina as Infantry cost is a bit weak, but once again a huge bonus and an additional benefit besides. +1 for free colonist. +1 for Cadet corp, as 5% tech reduction is the going rate. Finally, +3 for National manpower as 100% is way above the going rate of 25%, and the highest available. Finally, a +1 for synergy.
Nepal-6
+1 for 10% discipline. +2 for Royal Kumari. +1 for Leader siege. Arguable +1 for manpower recovery, as 20% is over rate. Finally, another +1 for synergy.
Ragusa-5
+2 towards both traditions, as they are nicely over budget. +1 for diplomat. -1 For reduced RR, as that's a somewhat trashy idea. +1 for synergy.
Najd-5
+1 for over budget conversion, and another 1 for leader maneuver. -1 for reduced stab cost, generally considered mediocre. +2 for enemy attrition, as it's a good unique idea but not on par with republican tradition. +1 for extra missionary. +1 for (conversion) synergy.
Switzerland-2
-1 for stability, and another -1 for the trash reducing war exhaustion. +2 for religious unity. +1 for fort defense. +1 for extra discipline.
Punjab-6
+2 for religious unity. +1 for extra production efficiency. -1 for stab costs. +1 for extra discipline. +3 for 50% morale (that's a lotta morale!)
Ming-5
-1 for 10% provincial trade power, as that's kind of trash. +2 for 10% ideas (one for over budget, two for being a tradition so maximum benefit). -1 for stab costs. +3 for manpower. +2 (arguable +3) for better relations.
Austria-7
+2 for better relations. +2 for diplomatic reputation bonus, above average but +2 diplo being sort of mediocre. +1 for edict as it's a two in one. +1 for diplomatic relations bonus, as an uncommon but good idea. +1 for synergy.
Ottomans-7
+1 for good rate tradition, +2 for reduced coring costs. +3 for Ottoman tolerance as it's a huge 2 for 1. +1 for Ghazi. -1 for reduced war exhaustion. +1 for above rate manpower recovery.
And for reference...
Generic ideas-MINUS 7
-1 for stab cost. -1 for poor tax gain. -1 for poor merc reduction. -1 for poor trade power. -1 for poor manpower. -1 for trade steering. -1 for poor production efficiency. Man, those generic ideas suck.
