Dang Sea, you come up with some good questions. I use a bunch of different mounts and for the most part none of them are anything the kits came with. Most the time the kits come with two piece mounts, nothing wrong with them at all but I find them harder to install correctly so I don't use them often. The number one mount I have used over the years is the Great planes adjustable mount. No reason other then every hobby shop has them in stock and I find them easy to use. It's that lazy thing I have going on
I can't recall if it was OS or YS that told me to use solid metal mounts with there four stroke engines? Been a while. They{?} told me that the four stroke case could crack from torque or expansion in a flexible mount?? Take that for what it's worth, I have been using the GP mounts for a lot of years and never had an engine case crack. I do have several solid metal mounts for four strokes though, for the most part OS mounts but they are great to use, all four holes line up perfectly with the engine, just nice to use.
I have several anti Vibe mounts of different makes, some I like more then others but yes, they really do keep the engine from shaking apart the air frame. My favorite is the one made by Jtec but if you want to use one on an ARF they aren't one I would advise. If you are building a kit then they are great because the fire wall requires some mods. They really work great though.
If people have found mounts that they like as you have I say just keep using them, if it aint broke why try fixing it!! If you have a plane that looks like it's shaking the air frame to pieces then by all means try a good anti vibe mount.
I follow no firm rules but I do have a number of different mounts in my shop. As I'm building I kinda give the engine some thought as to the vibration and size then rummage through my shop to find mounts for it then pick from what I have. I do try to use what I think will be the best mount but I don't over think it. {{Too Often}}
Good question!!! Can't wait to see the other answers.
Gene