Hi, I have been in rotts for a number of years, and particularally enjoy looking at pedigrees. Generally speaking dogs that have more so called 'european lines' behind them tend to very workable. Therefore they need more stimulation both mentally and physically. My first rott was fully german, although bred in this country. He needed alot more mental stimulation than any of my subsequent dogs. All of which have been 'english' for a minimum of four generations.
I think you are doing the right thing by trying to compare lines. But maybe you could talk to some breeders that are interested in european and american lines. Contact the Rot' Club or the Midland Rott' Club for some more information.
Just remember that rotts need plenty of stimulation, and time spent training, so can take up quite a bit of your personal time in the early stages. I hope that you come to the right decision, and if you do get a rotty, you'll have a friend for life.