Fly what you like. Personally, I've been avoiding any plane with an ENY under 15 lately, unless in a mission, or upping an occasional perk-ride.
I'm not that great a fighter pilot (better buff driver), but I earn enough in the high ENY rides to pay for the occasional 262 or Tempest.
Simple math: Your plane's ENY / Other guy's ENY = points earned. This is further modified by the perk point bonus, so I've been avoiding whichever country has a horde going in an arena.
15/5 = 3 points for me if I win. 5/15 = .34 points if I lose.
Keep flying those ENY 5 planes boyz and girlz. I'll take the points. More fun flying less used planes anyways. And challenging.
So,
No N1K2, but I'll take a Ki-84
No La-7, but I'll take an La-5
No Pony-D, but I'll take a Pony-B
No Spit 14, 16, or 8, but I'll try a 5 or 9 occasionally
No P47N's, but I'll take other JUGs
A lot of other nice rides with ENY's of 20 or more.