Things to consider: how long are your rides now and how long will they be in the future. MTB pedals are great for short duration but for the longer stuff not so good in the support department. If you are doing cross training i.e. walking MTB pedals are much better and easier to walk on as well as will last longer if you do. They can cost less as well. If you have a wide stance the adjustability of Speedplay Zeros can't be beat. look KEO are popular as well. Of the 4 I've used I like Speedplay the best. Great float, (side to side free movement) zero up and down movement, nice large base on the shoe, metal cleats so they last longer. On my cyclocross bike I have Crank Bros eggbeaters and they work fine for that type of riding.
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Sir Mark, Knight of Sufferlandria