I can’t say which one you should install but I can give you some information on both versions. Hopefully someone else will come in and cover anything I may miss, but…
(I’ve been out two weeks so my info may be outdated)
Last I knew, the 4.35 version was the current “official version” and updated plugins work with it. ( Like Reality).
Version 4.5 is still in beta ( I believe) and many bugs have been fixed as well as an improvement to the shader mixer (so I have heard) but the new plugins have not been updated for it yet because many are waiting for the sdk to get out of beta.
Well, that’s what I knew as of two weeks ago anyway…hope it helps you!!