Wow, that's a tough question. One of the things that makes LMP1 so awesome is the diversity of design amongst the different makes. I guess If I have to pick one favorite, it would be the Audi team. I have been watching sports car racing for over fifteen years now and Audi has been the brand most committed to the sport in this era. I have a lot of great memories watching them win so many ALMS races season after season. Back then, I would always cheer for the underdog teams, but I grew to appreciate over time just how awesome an achievement Audi's dominance was. Plus the various cars Audi campaigned were always incredible. I just wish I'd been able to start attending races sooner.
While Audi is overall my favorite team, my favorite of the current cars is absolutely the lovely Porsche. The 919 is simply stunning and the Porsche brand is legendary. Such a shame that the Porsche never was able to race in the ALMS as reportedly intended.
A final mention goes to Rebellion. Always a great fan friendly team and the winners of the final Petit Lemans, the very last ALMS race.
