my opinion would either be IR or an aircat. I stay away from the snap-ons because i just find that the snap on brand is overrated and very overpriced except for a few specialty items. As others have mentioned, the ir231 is indeed a badass in terms of durability.. very difficult to over abuse it. The titaniums are also very light, reliable and powerful impacts. hard to go wrong with one of those, or for any IR for that matter.
The aircats are quite the wrench as well. I have been using my nitrocat for less than a month now so i cannot comment on reliability, but i know a couple folks who've had it for a little under 5 years and no problems yet. It probably has everything the titanium has and more except for the IR track record and weight, its .5 lbs heavier than the titaniums, but anyway the way i look at it, i can get 2 aircats for the price of one titanium so even if after years worst comes to worst, ill never have had to spend over the initial amount for a titanium.
Theres a lot of choices out there, believe me its really hard to choose the right impact, sometimes even stressful because they are so diverse in so many different ways, but this is my 2 cents