My personal favourite of the 28f2,8's is a 1981 version III, but with the later hood with the cut-out for the finder. The two previous versions were not as good, the version I in particular was a bit weak wide open.
I did have the version IV for some years and it is probably the best of the 2,8's. The reason I disposed of that one was that I found myself going back to my III version all the time and I also had too many 28's.
My version III was boughgt new in -81 and I used it in Paris for a year and it has a certain sentimental value.
I did try the 28f2.8 ASPH and if I had to buy a new 28 (and it had to be a Leica) I would consider that one.
I did have the 28f2 Summicron, but I never warmed up to it. I found that I preferred my 28/1,9 VC when I needed that speed.
Also look at the ZM 28f2.8 - it has a nicer tonality in bl/w than the Elmarit's, but I dont know what it is like in color.
For small and compact, though a bit slow - nothing beats the VC 28f3.5. In bl/w it is one of the best lenses, period, that I have used. It is so good that I have stocked up on it -have three at the moment!