Wagerjunction is a good program, IMO. I've never had any problems with them. I'm sure others will pop in and let you know their thoughts too, but from my standpoint - they are good.
Very easy to get ahold of
updates sent via email monthly
payments on time
Affiliate manager good to work with and accessible
Marketing material up to date and creative
only draw back for me is they do not caterer to USA players.
Yeah, I'll add my voice to the WagerJunction love-in. From an affiliate perspective, they are very proactive and give you enough information to promote them properly.