I've used GnuCash for 13 years now, for personal finances and two companies, and love it to death. There's something really satisfying when you see everything balance!

The only issues I've had over all these years have been banks/credit cards that have weird idiosyncrasies in their file formats (lookin' at you, AmEx) that require you to remove the trailing white space (bad memory, I have a text file that reminds me what to do every time) or whatever and getting stock updates (gnc-fq-update) working again after upgrade.

It's also really accessible. While slow and a little annoying, I can do almost everything with a keyboard instead of the mouse (unlike so much online tax software, which is a carpal tunnel specialist's dream).