I can tell you that Deutsche Telekom has much much more aggressive sales reps than 1&1. (I've been with GMX/1&1 for ~15 years and with DT for ~2 years).
DT called me on phone over and over again, so much that I had to block them on my FritzBox. Several times they even knocked at my door.
DT called me on phone over and over again, so much that I had to block them on my FritzBox. Several times they even knocked at my door.