Without context your question is impossible to answer.

Do you want wood, wood-clad, vinyl, fiberglass?

Do you want casement, double hung, single hung, slider, awning, hopper, tilt-turn. fixed?

Full tear-outs, inserts, sash package?

Where do you live? Location matters.

@oberon476 I have the same questions. I am thinking of Pella Fiberglass VS Andersen Fibrex. Any thoughts on this?

I would steer far away from anything Pella were it me.

You don't like Pella as a company or you don't like their fiberglass quality?

Pella in general. Fiberglass quality is fine, manufacturer dependent but Andersen Fiberex is not fiberglass.

I agree with millworkman.

I prefer Andersen over Pella in general, but for fiberglass I would look at Marvin as my first choice.

Nothing inherently wrong with Fibrex as a window material, but its not fiberglass.