The 28 'Cron is an excellent lens. I bought this after acquiring the M8. But if you do not need the f2.0 speed, the Elmarit-Asph version is also an outstanding lens. If budget is limited, have a look at the 4th version of the 28mm Elmarit, non-Asph but capable of very good result.
i'm not sure i'd agree with the rest of the posters. Having shot the cron and elmarit for a while last year, i'd go for the elmarit unless u absolutely need to shoot at F2. In terms of sharpness and color rendition, i'd favor the elmarit.
... the Elmarit-Asph version is also an outstanding lens. If budget is limited, have a look at the 4th version of the 28mm Elmarit, non-Asph but capable of very good result.
i think that the 2h price for the elmarit asph and IV are about the same. but agree that either elmarit are good lenses, and so are the biogon and the ultron. of course, you can almost not go wrong with the summicron, other than it being more expensive... think the price difference is roughly 2k (or double) between a new summicron and an elmarit.