Welcome to FOG. I have the older Rotex 150E and the ETS 150/5 - there's also an ETS 150/3 with a finer stroke, more for fine finishing work, but I don't have that. The Rotex is part of my 'holy trinity' of sanders ((Rotex, Duplex, Deltex) that travels with me all the time, but in terms of use personally I prefer the 150/5 - it's lighter, easier to handle and just fits my hands better; I pack the Rotex with me because it can do more, and I never know quite what I'm going to be coming up against. Also, the newer version has had a bit of ergonomic work done, I think, that makes it easier to hold; there are plenty of Rotex users here, so I'm sure they'll be along to chip in soon.
Bottom line I think is that if you can only have one sander (for now, at least) then the Rotex is a great place to start.
HTH, Pete.
BTW, I think this thread may get more responses if it was in General Discussions rather than Tool Reviews - maybe one of the mods can move it if necessary??.