There are really only 4 collapsible Leica lenses whether in LTM or M mount. The Elmar, the Summar, the Summitar and the Summicron.
The Elmar was made in both a 3.5 and 2.8 version. The version II Elmar (2.8) is prone to internal fogging from the lubrication used on the iris. The collapsible Summicron is prone to cleaning marks on the front as the coating is very soft, it also often have internal hazing issues.
So, yes the Elmar is more prone to internal hazing than other Leica lenses.
The Summitar have clickless aperture but the Summicron have click at every half stop. The Summitar need a special adaptor from 36mm to 39mm but the Summicron have 39mm filter thread.
Not sure about the Elmars as I only have and old 3.5 LTM that does not have a filter thread.

If you have a choice go with a 2,8 Elmar or a Summicron if you can find them clean. The Summitar is good too with some character that the other two is lacking a little. The Summitar is a very good lens for the price.