I always felt both the step-through and right-leg-behind styles were important to know. Step through is best for fast dismounts coming into a flat barrier, for example, but the foot behind works better in traffic or slower spots where you don't want to trip over someone.
I also am a fan of running my brakes "backwards" because it helps the fast step-through dismounts immensely.
Oh, and I try to unclip the left foot early 99% of the time.
Whatever keeps your bike going forward with you upright, i say. I've used every method and crashed. I've learned what works for me now, and that is what i do (i swing behind my left leg, still clipped in). in tight packs i will unclip though, to avoid the pile up and lots of fingers being pointed at me.
I step through a lot but might go more Euro this season. If you take a look at the pros, they all step back. Tonkin says it's easy and scrubs a little speed going into the barriers.
I unclip when I make the drop to the ground. I try to exaggerate the motion so as to insure that I'll really unclip. I've only screwed it up a few times and not at all last season.
I know it's easy to obsess over technique, but the average Euro is looking to get a few more watts, not figuring out how to refine dismount technique. Spend the time to get off and on the bike without hurting yourself, then work on fitness. Over the course of a few seasons, your technique will get better as will your overall race strategy. The more you race, the better you will get.
high speed barriers can be easier with a step through. Many people claim you can carry much more speed with a full stride resulting from the step through.
So far I have yet to encounter any barriers set at locations where I'm carrying enough speed to warrant the step through. But I still practice it as part of the routine. One of the biggest advantages though with the step through is actually realized on the re-mount. When you step through and release properly the right crank arm is pointing just forward of the middle, ideal for jumping on and applying power. When you step behind often the crank is straight up and down.
I almost never begin a dismount unclipped. I always unclip as my foot is dropping off the pedal. If the course is extra muddy or there is sticky sand on there I will do a quick unclip-clip while pedaling to judge the ease of release. There have been rare isolated times when I have unclipped prior to begining the dismount but it is rare. I prefer to have the control of not being bucked off the bike on the uneven terrain just before the barrier. It saved my bacon hitting one of the chuck holes leading into the barriers at NoHo this past year.
I find that if you are braking in the middle of the dismount you are doing it wrong. The step behind is a fantastic way of slowing the momentum down to a sprint pace w/o the brakes. Another benefit of the step behind, it can be done a bit faster than the step through and keeps you pedaling and in control on the bike longer.
And yes. vanwacx is correct. To actually be competitive it is far more productive to obsess about the watts/power you can put out over the duration of the race than to worry how you are getting in and out.
Now if we were back in the good old days of cross - 98 or so - when there were barriers upon barriers... then the technique made a big difference... but with UCI regs the Portland area Six Pack will be an oddity.
Are there still any high-speed barriers left? No more six-packs here in the Midwest, that's for sure. Doubles inside of hair-pins seems to be the fashion.
Me: step-back, (push down on the top-tube to lighten the weight on the pedal at the moment of unclipping) unclip as I bail out, and then hit the ground running. Simple, safe, routine.
As for braking, do it early before the entering the dismount sequence. Knowing your optimum approach speed is what practice is all about. Although I do love to see racers that decide to "attack" at the barriers and dismount at a speed faster than they ever have tried before in their (short) lives ... sweet wreck dude ...
Back in the late 90's I saw a guy try to attack as he approached a triple set of barriers. It looked like he tried to take a few more pedal strokes, than couldn't decide if he wanted to step through or step behind. That moment of indecision caused him to get tripped up and he ended up landing on top of the first barrier with his top and down tube folded in half. Moral of the story, no matter which technique you decide to use, make sure you can do it going fast and slow, everytime.
I agree with the movement to reduce the chance of accidents by eliminating straight-running barriers. Especially with the growing number of new racers. Don't you also think that the straight-on-high speed barriers have been removed to eliminate bunny-hopping?
Last year was my first season. I started by not doing the first two things, and unclipping during.
Then I started stepping through more. I do agree with Adam though -- there's a time and place for both methods.
Then after bashing my ankle on my pedal/crank enough times I started making sure my 'landing foot' was well out of the way. I occasionally now unclip before the dismount, but mostly I still do it during.
One thing that I have to learn to do is to put my right hand on my toptube when I'm dis-mounting, rather than leaving it on my bars. It never feels 'right' to me, but at the same time I also often find myself scrambling for the TT while rapidly approaching a barrier.