First of all, I hope that when you say endgame, you refer to that stage of the game where King safety is not so big of a concern.
If so =>
There is really no rule of thumb or method to this. You descend into an endgame hoping to make best use of your position and material. More pieces on the board, more complications. Fewer pieces, fewer complications. No pieces and just pawns .. then it comes down to exact calculation.
Still, I think that I would like to have the addition of a piece. I just feel more comfortable.
Well whatever helps you enjoy the game better, then. It is quite natural for us to favor one kind of endgame over the other. The vast majority of intermediate players loathe Rook and Pawn endgames (me inclusive) though we try (as hard as we can) to study them given the frequency of occurance at the higher levels.
I am horrendous in rook and pawn endgames. Even up a pawn I've been known to lose. Heavy pieces in the endgame are usually complicated.
I definitely prefer bishops in the endgame as long as there's enough pawns on the board to promote one.
Unless things are really closed and locked up, knights can be somewhat slow and useless.
If you were facing a situation in the middle game, where you had to choose between bishops, knights, your queen, or rooks, which is the best in the endgame? For me, I would choose to have a queen trade, then trade off on of my rooks, and possibly my knights or a bishop. and obviously a few pawns.
Geez, where do I start. There is no choice that is correct in all circimstances.
Pawns both sides of the board? Bishops are better than Knights
Opponent has a passed pawn? Knight better than Bishop
Your're down a pawn? Opposite colour Bishops are good for you. You're up a pawn? Opposite coloir Bishops are bad for you.
etc, and bear in mind, all these rules have exceptions.
Chess is totally subjective to the actual position. Give some positional examples! 
imo the most important pieces are always pawns, if you get them into good places etc then they create the infrastructure for the rest of your army to maneuver while simultaneously limiting your opponent's mobility. This is key in every part of the game.
I guess some examples would be like equal pawn structure on both sides of the board, and maybe an extra peice or two.
I guess some examples would be like equal pawn structure on both sides of the board, and maybe an extra peice or two.
So you want an example of a clearly winning endgame for one side?
Ya, that would be nice. It is not as much me not knowing how to do it, just I would like to see all of your preferences.
I don't know whether to say I love bishops of opposite color endgames or that they drive me nuts. You just can't win if you're up a pawn or two, it's impossible unless it's a one or two minute game and my opponent is a nutcase.
The OP & thread title make little sense to me but I'm going to interpret all of it as "which kind of endgame do you prefer playing."
My favorite endgames are rook endgames as I feel like I do well in them.
My most hated endgame is the queen endgame, where any little mistake can lose you the game, or nullify your advantage by giving the opponent the opportunity to force a draw by threefold repetition. It seems very hard to make progress in some situations. Also, you must constantly respond to opposing checks & find the way to avoid giving your opponent the opportunity to make a double threat or force a draw on his next move.
I will agree that the most hated endgame is queen engames. They are very annoying, and you said the rest.
Yep! Queen endgames = NOT GOOD!
If you were facing a situation in the middle game, where you had to choose between bishops, knights, your queen, or rooks, which is the best in the endgame? For me, I would choose to have a queen trade, then trade off on of my rooks, and possibly my knights or a bishop. and obviously a few pawns.