There's no such thing as "the best".
It depends...
If you tell us the kind of rider you are, the kind of riding you do, the kind of frame you have in mind, and a sense of budget, then we can collectively tickle our butt holes and offer suggestions.

By saying the best, I mean that I am looking for a company that produces frames of proven quality.

As for what kind of frame I'm looking for, I'd like to know a suggestion for an endurance and maybe an aero out of pure curiosity, but I'm definitely looking for something reasonably comfortable.

I usually ride 50-70 km trails but 1-2 a month I go for 100+ km trails. Other than that the rest is daily riding around town to do stuff, run errands but for that I won't be using a new bike.

The budget I have is about $1500