Based on what is your playing style and of course it depends on how much you play as well.
Late game (Cold War Age) and frequent World War participants are mostly German and rightly so. The Fury bonus dps is a massive help for attacking and collecting ntgs
In lower ages the British (loot bonus + extra rifle range) and French (more mp battles per day, i.e.higher oil looting and ntg chance). The Koreans (and the Romans) are coming just behind these 3 nations, although there are here and there some bases, where the extra tactic could help... But as mentioned above - the economic bonus is less frequently used per day, and the same could be said about the extra tactic - you don't need it in mp, and for war it is questionable whether it really helps.
As far as the extra dps on the rifles... as you are advancing over the ages the defenses are getting by each age a higher dps as the rifles... there might be a sweet spot (maybe in Industrial Age) where this imbalance can be "balanced" by the Uni researches on rifles and the increased barrack size, but with the introduction of the Silo in the Global Age and later no significant improvement on them in Atomic and CWA makes them nearly obsolete - you cant group them well anymore (Silo) and when separated they can't handle well both the defenders, mortars and towers.
Furthermore since the sabotage, protect and betrayal tactic slots were doubled and the silo was introduced, the extra tactic slot lost its importance significantly (protect doesn't really help if the silo can't be handled early on, and 2 decoys for 1 sabo is a good trade in most of the cases). Heal, demo and betrayal tactics are rarely seen in high age wars. So whether you use 5 or 6 decoys(or even 7 or 8 decoys) is not a big advantage - considering the fact that you have roughly 1.5-2 mins to place them...
So for addicted players (more than 2 hours per day) I would recommend French or British (maybe I'd prefer a bit more the French) till CWA and a few generals are well upgraded, and then simply switch to Germans.
For more relaxed players just take the one you like the building and troops display the most