I've used Look, SPD and now Speedplay.

I would stick with SPD if I did not have that newly confirmed leg length discrepancy and the buildup under the cleat nixed comfortable walking in the Mountain shoes.

Look is not significantly quicker getting in, although the slightly weighted pedal means it is "in position" for you to engage most of the time. but it's one-sided entry only. Most SPD pedals except the "pseudo" roadie model, and Speedplay are double-sided.

Speedplay offers a kit to adjust for the leg issue and so I went for that: I really like how easy it is to engage, but walking on these is a cinch and I just got the cleat covers to make walking a bit more secure.