Thanks Jetboy for starting this thread. I have been thinking of starting a thread on this topic for a long time.
I have 2 of nearly every Forza Edition car, (and a few I have 3 of ). I love racing these cars just for the bonus CR. So the FE cars get the most race time for me. Favorites? I do like the Ford GT, even though it's not very competitive in it's class, 50% at Le Mans, oh yeah! I have 2 of them and one has a V12 in it! I also like the other 50 % cars, the BMW M4 and the Nissan GT-R. The Ford Cosworth has gotten the most drive time, as I enjoy racing that one on the Daytona oval and collecting the Stay on Track for Race MOD bonus. Lots of others I like as well, the modern Chevy Camaro, and the modern Mustang.
Least Favorites? The Monte Carlo, simply because of the look. It's hideous, (in my opinion). However it drives like a champ, and is competitive in it's own division. Also not a fan of the Honda Civic 97 FE. the one with the infamous flared fenders. In this case, the look isn't so bad. But performance-wise it is the worst car in it's division. The Subaru BRZ gets a vote too, I own 3 different ones all with different class tunes, but the low 15% bonus and the track it receives the bonus on forces me to throw that one in.
I do wish they had spread out the FE cars among other dealers a bit more. How many Ford ones? Also I would like a couple more 50% cars, balance it out a little. And lastly, the tracks where you get bonuses on. Top Gear?

Ugh! Test Track for the Ram pickup FE?

. Dubai for the Acura?

the Cadillac at VIR ???

. Some of them are lousy choices, not well thought out. No Cars with a bonus at Daytona? What about Rio? lot's of tracks there. No bonus at Homestead either. Yet there are a couple of tracks with 2 cars that offer bonuses.