I have used both Mobil 1 15W-50 and Lucas synthetic 20W-50. What I noticed about the Lucas, was that it is thinner and got pasted my rings and or valve guides. This was on a low milage '03 Road Glide.
I really like the Mobil 1 oil. I use it in my '96 Dyna with 60k miles on the odometer. The motor was rebuilt with approx 30k miles on it, due to cam bearing failure. This was before switching to Mobil 1. I switched to Mobil 1 after breaking in the motor. I tried Amsoil in the Dyna, and I really liked their product but it is hard to find.
Currently my 03 has 35K miles and is doing great using the Mobil 1 oil. Lately, I have been having a problem finding the 15W-50 grade. On a side note, I have a '87 Volvo turbo wagon, with 250k miles and it runs on Mobil 1 oil. The stuff works very well. Thats my .02 cents worth.