Read them both, compare which rules do what best, and Bob is your very kind uncle. There are some fundamental differences in certain rules (i.e., casting times and the breakdown of a combat round), so you have to go with what you prefer. MRQ is strong in areas such as Legendary abillities, and details rules for divine magic, where there is no provision for this in BRP (at least in the main rulebook, I think there is a monograph of divine magic), and BRP is strong in its clean combat system, backgrounds and GM tips etc., plus a nice rules section for Apotheosis and a non-hit location option for combat. Ive successfully converted MRQ spells for BRP, and regularly use a combination of the bets bits.
I'd be interested to see what you think of a comparison.