As Alex has said, software is software, and at the end of the day all offer some level of improvement but have slightly different approaches as to how it's delivered.
If you want something you can load on / load off then maybe a Superchips is best for you, but I've never been totally convinced by the overall power gains based on people's responses (& industry insider knowledge about how short their development windows are for each map). I'm not sure that Superchips offer a multi stage upgrade (e.g. stage 1 /2/3), but I think there is some customization they can offer and they send you files by email.
If you want something that you can configure, then Revo is a good choice as you can get an SPS which allows you to adjust the boost / timing / fuelling, set an anti theft mode, turn the map characteristics on/off. This presents a broader range of options if you go on to do other mods as you can tweak the map settings. When it's really warm in the summer you can dial back settings to compensate for high ambient air temps, then ramp up again once the fresher weather arrives. Revo do 2 maps, an aggressive map which is feels more urgent, and then the 1:1 linear map which is more progressive depending on what kind of feel you prefer. Revo do stages 1 - 4 taking you from 300bhp up towards 500'ish, so there is quite an upgrade path on offer.
Shark offer a very good service with an increasing number of dealers around the country. I know they can supply a 'box system' offering, but I'm not exactly sure how it works so I'll leave the explanation of that to someone who knows what they're talking about! Shark also do a multi-stage offering, and of the people who post on here all seem genuinely happy with the quality of the mappings they receive, so it's another sound product.
APR have been around for a while, but I know very little about them and you'd have to do your own research. Owners rave about it, but then you could say the same for most of the above.
MTM have recently dropped their mapping prices but remain the most expensive, but have a benefit where dealers like Audi Glasgow won't frown on you for it as they supply cars with MTM maps from the dealers.
You could go the indy route and get a 'bespoke' map (like MRC for example), which some will argue is the purist route to getting a map that suits your vehicle.
One thing that's REALLY important to remember is that when you do choose, try and select a tuning house that can support you if things go wrong. You're putting your car under extra stress and therefore you'll get the odd niggle that Audi obviously won't be able to fix for you. Having a good relationship with a tuning company (like Alex has with AmD for example), buys a lot of credit in your favour if you have issues. Choose a few dealers that's aren't at the other end of the country, and then go and visit them and see which one wins your vote. Double check their reputation on the net, and then if it sounds good, irrespective of what mapping franchise they offer you then can't go far wrong.
One final tip; ALWAYS be suspicious of anyone / any tuning house who tries to rubbish another tuners maps, I'd be more inclined to go with a company with an impartial view who sell their business to you based on their strengths, and NOT other tuners perceived weaknesses
You took the words right out of my mouth.....snigger.
