Not trying to be a shill for Seeking, but my experience with other sites has been extremely negative. I tried AFF for a month and it was a total waste of money. 1-2 chats, but nothing beyond that. And the number, variety and quality of girls paled in comparison to SA. On top of that, a lot of profiles on AFF seem to be dormant. A few weeks ago, I did a search on AshleyMadison and almost wanted to throw up. The profiles on that site can't hold a candle to SA. But if someone has found a site with better results than SA, I'm willing to look into it.
My approach is to get premium membership for about a month and get as many contacts as I can. Even if nothing happens during that month (due to my schedule or theirs), I can text them and cultivate the contacts later. I do that about every 6 months.
My biggest problem with SBs is that, with one long term exception, I rarely repeat. And if I do repeat, its usually not more than 3X. If I had to state the reasons for this (in rank order), they would be: girl was a disappointment (either looks-wise and/or not worth the asking price), no chemistry, incompatible schedules, too far away, or tried to pull a fast one (e.g., shorting on time). So mostly its a lot of work with mediocre results. Which is why I largely prefer AMPs.
If I lived in a big city, it might be different. But I'm out here in the hinterlands.