@sabi 300 baud with my Commodore 64. It came with a trial subscription to a commercial service called QLink, which (IIRC) was a predecessor to GEnie or one of the later generation commercial things.
Later, when I had an Amiga 500 with a 2400 baud modem and a CompuServe account, I'd often connect at 300 baud anyway, since it cost extra to connect at 2400 baud. I still managed to run up some eyewateringly large bills.