I’m partial to the Galaxy class. It’s big, sleek, and luxurious, which is great for when you need to be diplomatic. “Join the Federation! We have abundant resources and advanced technology, like this cool starship.”
For when you don’t need to be diplomatic, it’s also got plenty of firepower (enough to melt 20% of an unadapted Borg cube in one phaser blast) and speed (it can soundly outrun a D’deridex).