What style is the house?

we are replacing the baseboards of our ground floor

Why?

We are not replacing the door casing

Why not?

Do you also have crown molding?

We have a traditional style house. We’re replacing the carpet with hardwood and since we removed the baseboards we might as well replace them. We’re doing it ourselves and I was thinking that replacing the door casing will be too much work at this point. Although my husband did suggest to replace them. And no, we do not have crown molding.

The baseboard sample against the wall in this picture is 5.25

Your image brightened up.

Your trim will look best if the pieces look like they are part of the same set. The profiles will be similar.

It's more work and money, but I'd suggest replacing all the trim. About 5" for the base and 3-1/2" or a bit wider for the casing.

Your windows have picture frame trim, which is a builder favorite, but a sill and apron looks better.

You can add a backband to your existing trim, or to new trim to give it more presence. It would go all the way around, unlike what is shown in this picture.

I would replace the trim, with something at least 3 and a half inches, and a style, that matches the new baseboards. I like the ones you just posted a picture of. They look very nice.

With those ceiling heights, I'd lean toward the 5.25 inch base. 2.5 inch casing next to it can read a little light, but there's an easy fix that doesn't mean replacing the casing: add a backband to the existing casing. It wraps the outer edge, makes the casing look closer to 3.5 inches and gives it more depth, so taller base looks balanced. The most important detail is thickness. Your baseboard should be slightly thinner than the casing where they meet, so the base stops cleanly against it instead of sticking out past it. Check that on your samples before you buy. Also keep one base height throughout the floor rather than changing it room by room.

Ceiling height is a useful starting point, but I’d choose the baseboard as part of the whole trim composition.

Mock up both samples at a doorway with the existing casing and finished floor height represented. Compare their profiles and thicknesses as well as height—the base needs a deliberate, clean termination at the casing.

If the taller sample makes the casing feel slight, a compatible backband may be worth testing before replacing everything. One consistent baseboard through connected rooms will usually look calmer.

How thick are the existing casing and your two baseboard samples?