If I were to buy Bachmann (only did it once), it would be in their Spectrum line. Generally, they are quite good, although some kvetch about their Spectrum diesel products.
I know that the best rated steamer is their 2-8-0. Right up there is their heavy Mountain 4-8-2. It is all metal and heavy, and a good runner. I would guess that their Spectrum K4s from the Pennsy, a Pacific 4-6-2, is also a good runner.
The Dynamis should be a decent system, although I wouldn't buy one with less than 2.5 amps potential. If the Dynamis can do that, or 3 amps, or you can add boosters as you need to, then go for it if the price is good. It is made by Lenz.
The Sound on Board Spectrum engines have a degraded/non-full featured Soundtraxx Tsunami variant decoder. I have no experience with them, but they must be okay because the Tsunami steam decoders are universally liked, minus a few problems that one or two may have had.
I purchased a "new in box" Spectrum J Class 4-8-4, DC, and had a Tsunami 'heavy" added to it. It was a poor performer. It lurched at speeds less than 25 scale mph. My repair guy finally gave up on it, saying he couldn't figure out how to make it run better. That, as I alluded earlier, was my only experience with Spectrum Steam. I now have a BLI "Stealth" DC J Class that looks much better. And it runs well, too.