I thought about going with the 01/02 Parkhurst Vintage Series Milt Schmidt, as that is the first card I think of when it comes to the old BAP days, and I believe the first autographed card that I ever pulled.
However, to me, the best card that ITG has ever produced is one that I could only wish I could own. This card is arguably the one that put Dr. Price and the Be A Player/ITG brand on the map and generated a huge amount of discussion and publicity for the hockey collecting hobby as a whole. This card is owned by one of our very own members (webotew), I hope they don't mind that I pulled the scan from their show and tell thread, but it is the only example I could come across in my image search...

2000-01 BAP Memorabilia George Vezina Pad
There have been may other Vezina GU cards in the years since, and there may be other cards out there that are fancier or more flashy, but nothing as iconic as this particular card, IMHO.
-Rob