I don't know Quasar. I have used gnucash for a log time. I have run a consulting business, a non-profit, trust management, rental properties, and my personal accounts with gnucash. It works very well if you understand double entry accounting and the fundamental accounting equation - assets = liabilities + (income - expenses). I have a/r and a/p accounts, but I did invoicing and inventory outside of gnucash, so Quasar may be better suited for your application if you need those features. Gnucash has all the business functions except inventory; I just don't use them.
I would suggest taking an accounting course or two at a local community college so you understand the fundamentals before you embark on keeping your own books.
Mark