Merchant credit card service

Any suggestions on which credit service you would recommend. I had tried Costco's and I have been getting a run around.
I have one property and a 3 to 4 month window to rent.
Thanks

I have been using the Lynnbrook Group, and everything has run pretty smoothly for me so far. https://www.lynnbrookgroup.com/

I'm also a satisfied customer of Lynnbrook, although I've not had any situations that would really require anything special beyond set-up (no chargebacks--yet, anyway).

That said, I've heard good things about Costco's Elavon solution and have been tempted to switch, but honestly I don't do enough volume directly to really make it worth the pain of switching.