Hi Marcus, welcome to CAP 
As Dominique mentioned in various threads, don’t put all your eggs in one basket, so I think it is better to sign up with more programs.
Slotland is great, they are always among the first who pays affiliates in a given month.
I am working now my casino site, and pick the partners from the “X month comission received” forum here. 
If they pay constantly I read their T&C-s, and search for the program’s name in the forums here and after the ton of info about the group I can make my decision to work with them or not. If a lot of affiliates tell good things about a program then it cannot be bad.
I prefer to sign up more programs, because I would like to show my visitors different games and places, and when time goes by and I am not satisfied with one of them then I give them less exposure or drop them.
Hope this helps