Well Paige, I tend to like what I have actually seen, and also like modern road names too. So my list is Conrail, Norfolk Southern, Penn Central, Lehigh Valley and Reading. Though BNSF, CSX and CP Rail and are right after the first five.
NOW, my problem is I'm a 027 guy and I do this hobby on a budget. So, I had to learn how to repaint. Started with kitbashing and painting Plasticville buildings, then junker trains and quickly my skill levels were right to proceed to new items. And the current lack of O scale decals has not hit me as hard, as I can use larger HO scale decal heralds and logos.
I've also had to learn to be happy with the limitations of 027 curves. Obviously, bigger locomotives won't negotiate that curves and even if they do, they look out of place. So I have Alco FA's done up in Conrail, Norfolk Southern, CP Rail, and CSX even though that particular model locomotive has long disappeared from Class A railroads.
Some folks enjoyment of the hobby is prototypical fidelity, and that's cool... seems to be the recent trend. For me, my approach is like watercolors or impressionist paintings. I don't mind a "replication" and have learned to be content with that. AND I still have fun with it!
Some might disagree, but for me, a small layout is better than NO layout. Life is a compromise as is the train hobby for me.