I'm personally satisfied with Good Company and don't really feel the need to try out any others. But YMMV obviously.
How have you balanced signing up for cards with actual good signup bonuses vs cards that the good company pays you for?
A lot of the cards that seem to be on the good list a few pages back are from issuers I've never bothered with.
For context, I have a long credit history, lots of cards from lots of issuers with lots of CL. This is a result of an intertwined credit history with my Dad who shares my same first and last name, a good engineering manager salary, and playing a variety of credit card games for probably 20 years. So now I already have pretty much as much CL from all the usual issuers that I can probably get given my credit and income situation.
It's also my opinions that a good piggybacking card is worth more than a signup bonus to me, and that the posts here opining on which cards were good/better/best/worst did not line up with my experience and personal preferences.
I've also decided that the "app-o-rama" approach that was popular a while ago doesn't work well for me any more.
Finally, as noted, I'm happy working with Good Company exclusively. (If there were another trustworthy company that took cards I have that Good Company didn't/doesn't, I'd consider them.)
So what I do is every year or so, sit down and see which issuers Good Company supports that I don't have cards (or enough cards) with yet, and then see if there are any sign up bonuses for those cards. That's how, for example, I ended up with a Barclays AARP card. My previous Barclays hit the lifetime limit and I needed a replacement to start aging, and the AARP card had a $100 SUB on it.
But yes, I'm past the major issuers now, so I'm opening cards with the less common ones. For example, I've recently got cards with NFCU and TD Bank, among some others.
Finally, personally I'm not scrapping for every nickel any more, so I'm aiming for a situation where I can have a lesser number of cards actively piggybacking with a higher dollar per slot commission. It's the same work either way, so I'd prefer to get paid $200 per slot rather than $50 or $75.
As a consequence, I'm not really growing the number of cards in my piggybacking collection at this point very much. I have six cards that don't piggyback for various reasons, 11 currently enrolled, and 5 that are aging and/or need work.