So I was being cool and playing with myself  when I arrived at this position:

It got me thinking about 2 rooks vs 3 minors - is one set better than the other? What positions would favour the rooks, what positions would favour the minors, and would they ever be totally equal? How much difference does interchanging the minors make? Is 2B+N best? Thoughts!

Here, the rooks can't attack anything and after ...Nxe5, I'll take black anyday.

It's difficult to give overall pointers : I'd say the main factor is the nature of pawn weaknesses, and if the rooks can attack the opponent's king.

And yes, 2B+N overall is better than 2N+B

The rooks here look very ineffective because of the lack of targets as hietnunc said.

The better material imbalance is the one that coordinates and works together better, and most of all has targets. Sometimes a queen vs two rooks is useless, while the rooks can often work together on say the 7th rank while defending everything, but if there are lots of loose pawns that can change everything. In that case the queen's versatility could very well allow these pawns to be picked quicker than the more straightforward rooks can defend them (queens can attack diagonally, rooks of course can't defend diagonally), and in picking up some pawns the guy with the queen can make an offensive strategy based on advancing them, even if the king is too well defended. Also if the king is open, sure the queen can't mate him alone, but having tons of checks always comes in handy! In fact if you have enough of them you can safely play for the win and when things look bad take the perpetual check!

Elubas said it best so far.

While Hicetnunc is right, overall pointers are difficult...but, how do you think we developed opening theory? General principles that should just be followed.

If there are open files for the rooks to travel on, weak pawn chains or even a blockaded pawn (any sitting duck) then the rooks may have a better chance. If you're up against a pawn chain thats 4 long, 3 ranks away from queening, you're in trouble.

As for the 2N + B, or 2B + N...if its an endgame the bishops are probably better,  HOWEVER. Two knights can protect/attack 16 squares at a time...whereas, Two rooks may be able to cover the entire straight line, they only protect/defend 4 squares each. The bishops will only show their strength if there are open diagonals to work on. As you lose your pieces, I would start to take note of how the endgame pawns are looking so you can better evaluate what you need, and what you don't.

Also, two knights can straight up block a rook out of an open file, whereas two bishops cannot work together to 'clog' the file, even if they can protect each individual square a rook may want to move too.

We all know a Rook on the 2nd/7th is HELL, so its your minor pieces job's to stop them from getting through.

Also, as soon as one rook goes down, the other TWO pieces will have the edge. I don't care what the position looks like as much if I've got a straight up piece advantage. Obviously, use it to do whatever you need atm. Two rooks are MUCH stronger than one rook. Any 1 piece on its own isn't much of a threat in an endgame, there's just not a lot of mate material. They can pick pawns all they want, but if 1 gets across they're done. Its a lot harder to stop pawns and pick em off, even if they have a weak pawn chain or the king is exposed when you've got TWO pieces defending to your ONE rook attacking.

Just my two cents.