Welll this reeally is a personal preference question if you ask most. How I see it is as follows
#1 Look and for that matter SPD-SL pedals have large platforms. Easy in and out and distrubutes your weight more evenly than the smaller systems.
#2 The SPD style pedals can be used on either side where the look and SPD-SL pedals can only be engaged on one side.
#3 The large plastic cleat of the Look SPD-SL is easier safer to walk in if you ask me. The small metal cleats on the SPD style can and do destroy floors not mention are very slippery. I really like the rubber pads on the SPD-SL cleats.
Most shoes that take SPD's have recessed cleat mounts. They're actually much easier to walk in than LOOK type shoes. On my cheaper pair of SPD shoes, with the cleat installed, I can even do short jogs in them.
Orbea Enol roadie, Fly Micromachine BMX, Fort Track fixed
Cost is entirely up to you. SPD-SL and Looks both start from about £40 and go up to £125. I recently was in the same situation, and I went for the 105-spec SPD-SLs (£40, black, Ultegras are £80 and polished, DA is £125 and brushed ally). SPDs are better for walking than Looks and apparently Looks can squeak when riding. But Look cleats are compatible with lots of cheaper clones, SPD-SL cleats only work with Shimano pedals. It's your call. Check out my other thread "Looks versus SPD-SLs".
I've always had SPD cleats and have had very little (if any) problems walking in them. I wouldn't recommend them for walking around and shopping or whatever since the sole is generally VERY stiff and can become uncomfortable when walking long distances. Outside of that, I like the spd-style cleats.