A design-build operation usually has a competent designer on staff, or they won't stay in business long. Many landscapers on the other hand, do not have a clue how to design landscapes, even if they think they do. Yet some do and are very competent. You must examine a prospective landscaper's ability to design before you assume they can do it. Actually, you must look at any designer's ability because, as a group, they are all over the map on their ideas about landscaping.

There is no compelling reason for one over the other. It's still about the quality and price of the product that is being offered and the follow up given post planting. If the designer is not also the installer it is a team job no matter the business arrangements. If a one stop design install landscape company makes you more comfortable that's perfectly fine too

Thanks for the insights. I guess
It’s like anything else, some much better than others regardless of what titles they carry. You answered exactly what I wondered...is there any reason to go one way or the other. Thanks.

In my area, it’s very common for any service provider to promise the world then not bother to show-up. Then those that do show-up assume price is no object. Plenty of work for everyone so I deal with that.

I’ll ask for direct referrals from people in the area and go from there.

One way to find a lead on a designer, if you see a landscape you admire, ask the owner who designed it.

Portfolio, personality fit, and client references. There are multiple, valid ways to get to a successful landscape. Looking at those three things can be very telling.