I started with RQ2, which I liked just fine, but it always felt a little incomplete ... but I like my games crunchy and detailed. So when RQ3 came along, offering a lot more "crunch" and (mostly) refining what I already liked about RQ2, it quickly became my favourite system.
However, as we all well know, as a way to game in Glorantha, RQ3 was a disappointment for a long, long time. It wasn't a huge deal -- the existing RQ2 supplements were still perfectly usable -- but the lack of anything really new for Glorantha was frustrating. That, however, is a separate issue from the system, which compared to RQ2, was lacking very little -- other than some desperately-needed errata which, again, was a long time in coming (at least as officially published -- fortunately very early on I had a long list of questions that had been answered by Greg and Sandy covering everything I considered important, touching on many topics that the official errata remained silent about).
One funny thing that sticks in my head is that I noticed quite quickly that the rules version of the HP-per-location chart didn't match the stated 40%-33%-25% breakdown in many areas, which just didn't make any sense to me -- so I wrote a simple program on the university mainframe to print out an accurate chart. Nowadays, of course, it's comically easy to do the equivalent in Excel.
After some time I of course came up with all manner of house rules and extensions (particularly for combat) which I compiled into my own personal "RQ3.5". That document has a lot of needed work remaining still, but with the imminent release of RQG I don't see much point in completing it now. I'm sure I'll adapt many of those house rules into the new game. It's what we do!
As for other versions ... like many people we got a chance to look at the draft RQ4 and liked many things in it, but never made any attempt to play it. And there things remained until the first Mongoose edition was released. We tried it and we hated it. Hated! There were one or two interesting ideas that I contemplated retro-fitting into my RQ3.5 but motivation was a bit lacking at that time. I hear that Mongoose's 2nd edition was a considerable improvement, but the 1st edition had destroyed my interest in it pretty thoroughly. (I wasn't wildly impressed by Mongoose's publication strategy, either.) A little later some of my friends tried RQ6 and were generally positive, but I never got a chance to see for myself and had pretty much dropped out of the whole RQ thing (and role-playing in general, to be honest). I thought I had lost all interest in Glorantha, too, until the announcement of RQG proved how wrong that was ....
So I await RQG and the associated publications to see if we really have gone full circle over nearly 40 years ....