I use gnucash and have for 15+ years.
advantages:
* I think it is the most "technically correct" package I've seen. It uses generally accepted accounting principles and double entry bookkeeping.
* it forces you to really think of things correctly: expenses, income, assets, liabilities. Other packages sort of clump things into categories ... and that has disadvantages
* if you're a bit of a hacker, it's a dream package. It writes everything on the back end in XML or SQL. It makes it very easy to do some really cool stuff. I have hundreds of graphs I generate myself -- some going back 20 years (yes, that's longer than I've used gnucash, but I imported data).
* free, free, free
* runs on any platform but very well suited for Linux, since that's where it started
Disadvantages
* it's not as whizbang slick as some other packages
* it's auto integration for logging into accounts is going to be less than other packages. (From a security standpoint, I see this as an advantage, but I realize not everyone sees it that way.) It does have some abilities in this realm, but I have never used them, so I can't really comment on how well they work.