Mmmmm.
Well I like Look pedals for the road, as they have a nice big platform, and are really popular, so you can borrow other peoples bikes for a play.
Off road - I had SPD's but they used to clog up something rotten in mud and were no use. So I swapped to the Time ATAC's and they were fine - never clogged up.
If you aren't gonna race in the mud on her though - it's a toss up between SPD's and ATAC's for me.
Most MTB shoes are compatible with both SPD's and ATAC's - v similar cleat.
Bourne have some Adidad MTB shoes on offer now ! ;-)