I find Neteller payments the most convenient. They have a debit card, and you can just transfer funds to your debit card and withdraw from any ATM.
If you concentrate on just a few programs, you will qualify for making a higher percentage commission as you grow your player base. That, of course , is an advantage.
If you promote a lot of different programs, you have the advantage of not having all your eggs in one basket, you are more independent, and it doesn’t kill you when you need to drop a program for some reason.
There are a lot of pros and cons, and there could be some interesting discussions around questions such as: When a player comes to your site, is s/he more likely to make a decision to play when only a few casinos are represented in depth? I think possibly.
Are they likely to return to find another? More likely they will prefer a site with a large selection to revisit.
The more you think about this topic, the more criteria come to mind.