These three are all closely comparable. All three of these use different dynos.....go figure. Even though GIAC uses a Mustang and then calculates crank HP from that...when mine was only stage 1 GIAC, mine could beat APR stage 2 in the 1/4m here at VW Drag events. So it's questionable as to which is best based on their posted numbers. I usually recommend which have a dealer local to you and do you like their service. There's also revo technik...but dealers for them may be limited...unless they now have a self-loading deal for you. I do not believe COBB went back to the 2009 EA888, but you could check that one as well. A final option you have is a custom tune suited to your build. United Motorsport (or other custom tuner) may be near you or have a dealer near you or they may not be too far away.
Here's the three I mentioned...APR boasts the most. Some tuners do not like to over estimate power figures because of backlash from a customer if those numbers are not met. So you will find one tuner may post the most power they see...another may post what they know they can achieve on any car...and so on.