mostly zirconia and peek with some glass and rare titanium abbutments.
Ti bars I think I'll print at the local " shop "
I'm not a huge fan of grinding glass unless it's for rush cases here and there, but I think all three options are just fine. If you were doing a ton of grinding I'd have some different recommendations.
I'd look into the titanium abutment preform options with each milling machine and make sure the fixture and per part cost makes sense, all three are different and will allow you varying levels of flexibility and cost for this indication. Oh, also CAD support. For example, if you are using Dental Wings you cant mill preform abutments in the AG Motion 2, the CAD output isn't supported but ExoCAD and AG Mind is supported.
Zir and peek are pretty easy and straightforward. Hope this helps, good luck