If I had to chose between Buildium and Quickbooks I'd select Buildium because it is setup out of the box for rentals. This means that you don't need to create new accounts, like rent, and expense categories that are specific to rentals and real estate, but Buildium is expensive and for people with larger portfolios. However, as Dan pointed out Buildium is a property management software with an accounting module.
These aren't your best options for accounting and tax software for real estate. You should also consider Stessa and Digb. Both are real estate focused and setup out of the box for real estate so unlike Quickbooks you don't need to reconfigure everything yourself (or worse pay someone to do this). Unlike Buildium, they aren't property management software. Digb also includes tax filing so this is one of the differences with Stessa. Good luck!
