Interesting. Good luck. 
Still, Shield Management VI.
Toss-up between Navigation and Thermodynamics. Either one is deceptively simple but goes incredibly far.
Thermodynamics I can get. Not so simple, and yes, the overload is valuable.
Navigation? Kinda role specific?
Iād love if CCP did this and allowed us one level 6 skill, checking to see what would be completely broken and there really isnt anything, The idea of being able to spcialize hard into something is amazing even if its like 200 days of training time for a lvl 6 haha.
Lol this one
Astronautic Engineering 
Probably Gallente BS VI for neutron blaster/large rep reasonsā¦ 10% more dmg and 7.5% rep on a Hyperion that costs 100 mil to lose sounds great!
Minmatar Offensive Sub to VI would give 17.5% dps+alpha on those already mean medium arties thoughā¦ Along with 10% optimal falloff and 7.5% tracking.
This is a really hard question thoughā¦ Maybe 5% CPU Management would be better for all round, but thatās boring along with any other core skill.
Iām so boringā¦ Scrapmetal Reprocessing VI, or Command Ships VI
No wonder Iām solo(w) and unrecruitable after 14 years.
Itās already there, Bittervet VI and VII is in the queue
Iām surprised no one said assault frigs VI for the sweet retri buffās.
Nah, if you are, in theory, going to spend over 6 months training one skill, youād have to be really dedicated to that one ship to pick something as specific as assault frigs. A lot said (faction) cruiser, which makes a bit more sense, and I would be tempted.
But no, shield management vi would have the most return, for me. I would expect most players to pick something with the same rationale, though, with that huge a theoretical investment of time.
I guess it depends on what you fly the most as well as your activities. Any of the racial ship skills will effect a lot of ships in that class, pirate and t2 ships included. Where as t2 ship skills will cover all races but only for that specific type. Some of the core skills will effect all ships but to a lesser degree.
Swap it to Paranoia VI and VII is in the queue and youād have gotten it right.
Shitpoasting
Advanced ship toasting
couldnt even spell it right 
As the old saying goes
āItās funny when they donāt knowā
Biology VI
20% extra duration on booster effects is probably the one I would go for just to make more use of attribute boosters. After 100m SP and when notifications of āSkill Training Completeā only come in once a month does all skill training get boring. Itās just a long wait now and getting longer and more boring.
Many skills arenāt worth training to V, which is good, but some are obviously necessary and leave one no choice. Having a sixth level of the later means that everyone will want to train them, which means the ground will be levelled after a couple of months anyway. So obviously skills like Navigation, Shield Management, Mechanics, etc. will get trained to VI as soon as possible by everyone.
A better question could be ā¦ If CCP were to remove a 5th skill level, which one would you give up first? ā¦ I guess I could live with 4 instead of 5 drones if the balance remains right.
You are taking the sad and serious face, on a game thatās built to make people smile and create good moments.