Exch bishop for rook, or take knight - which?

I was recently in the happy position of being able to win a rook in exchange for a bishop.  But then my opponent made a move whereby I could capture a knight instead -- without losing my bishop in the exchange.  I took the latter option -- keeping my bishop.  Do you agree?

I think for me it would depend on the position and the tactical advantages of either move. Nothings in a vacuum on a chess board. Could you post the position? 

Depends on the position, material on the board, and pawn formations. Not all exchanges are equal.

Good online article -

The Evaluation Of Material Imbalances In Chess

by Larry Kaufman

posted by Dan Heisman

I should have mentioned in one above all things being equal -- position-wise.

I realise individual positions might have an advantage by accepting the less advantaged option.  But all things being equal -- which?

Thanks Estragon.  That was my thoughts at the time.  Thought I'd check as that or a similar option might recur.