my broken in belt is just now feeling broken in for real, 9 months later.
I have both. Get the soft.
Not that I'm any authority on anything strength related, but I just wanted to add that Dean recommended the soft one to me, and it was instantly useful on workout 1. A few weeks in, it stopped causing bruising of any kind.
I'd highly recommend it.
I haven't tried the stiffer version, but I ordered the soft athlete belt last december - and it is the best weightlifting belt I have ever used (had an inzer prior). For reference - I used the inzer for about 2 years, and the best belt felt more broken in on day 1, then the inzer did the entire time I used it.
I would call dean, instead of ordering over the internet. He can punch the holes custom to your waist size, instead of getting the generic s/m/l/xl.
I have a 33inch waist, and the belt fits me perfectly on the exact center hole, with 4 holes on each side.
To expand on the customization I was a fat ass when I ordered the belt so he have me 6 holes on the thinner side, 4 for more fatty. Only issue is 3 months of rfl made me smaller than the 6.
I got the stiff version about 18 months ago. Took some getting used to at first but its fine now. Squatting with it 3 times a week, and deadlifting 1-2 times a week broke it in fast.
I recommend giving Dean a call and getting a customized belt for the same price. He'll get you to explain your current training, where you're headed with it, etc and make a recommendation from there.
edit:
If you'd rather just order one I'd go with the athletic, broken in (soft), single prong.