I have ridden SPDs for about three years on my fixed and have unclipped about twice in that time - both times when I was trying some kind of skid for the first time and twisted my foot. They will only accidentally release a lot if the tension is very low or your feet slop around a lot. They are very easy to clip in to, especially if you are already used to them.

I now have Time ATACs and they feel more secure than Shimanos. I think this is because the release angle is greater and maybe because the binding system is better designed. I got ATACs because concensus on this board for the past few yearr has been that they are the most secure, especially for brakeless fixed riding. I also looked at MTB review sites and boards and there is unanimous support for ATAcs working well and being built to last.

I have heard a few stories about Eggbeaters breaking in various ways, although this is always allied with Crank Bros excellent customer services. I have also heard that the "unclipping point" is much less defined than SPDs or ATACs and so that might take some getting used to.

In summary, if you are used to SPDs and have them already then you should be fine. I moved to ATACs cos I got some at half prce and would say that they are better, but that SPDs are fine too.