I have a dozen or so Weaver engines, both steam and diesel, and I like them a lot. Weaver has the best service in the industry, so you can be sure of help if you do have a problem. Here's some information that may help.
First, I assume you are talking about older Weaver engines, since you mention QSI and Proto. First, Proto-Sound is from QSI, not Lionel. It is similar but not identical to MTH Proto-Sound. QSI licensed or sold various versions of Proto-Sound to different OEM's.
Weaver engines have been available with the basic, licensed version of Lionel TMCC for ten years or more, so you will find four different sets of electronics in Weaver products: TMCC, QSI Proto-Sound, QSI OEM (a predecessor to Proto-Sound), and plain conventional operation. Some of the plain ones have a horn and some have no sound at all.
My experience with Weaver engines is that all the diesels and most of the steamers are good strong runners. The QSI versions have the usual weaknesses of all QSI products, mainly battery issues and undersized power supplies that can overheat if you pull long trains for long periods of time.
Some of the Weaver steam engines have issues. The brass ones are subject to the usual production variations of handmade brass locomotives. You can run into production defects that affect operation, such as loose motor mounts or whatever. Older brass engines can be a great bargain or a giant headache. I've also found that the Weaver die-cast 2-8-0, while it is a good puller and runs well at track speeds, is not great at low speed. I'm told that adding an ERR cruise control fixes that issue.
Some older Weaver diesels have a single, central motor with chain drives to the trucks. I have no personal experience with those. I actually own one but I bought it mainly for display and I've never run it. The newer ones all have the usual twin-motor configuration.