Hi Todd, there is already a registered Todd in the forum, but he must be sleeping by now.

-chen and -lein are synonymous
I have a slight personal preference for -lein, since it corresponds to the Swabian -le
The use depends a little on the main word. The pronunciation of Höslein ist more obvious, although Höschen is very common. Or Häuslein and Häuschen. In Swabian it would be Häusle. And Mäusle, not Mäuschen.

No idea about -el. Probably used in Bavaria and Austria.

Only -chen and -lein are usually used in formal text.

Does that help?

-chen is probably more widespread in "hochdeutsch", which is reflected in the LEO entries (search with *chen, including the truncating *).

Generally speaking, I would say that "-chen" is nowadays the most commonly used diminutive in everyday language, whereas "-lein" (to me) has a certain "old-fashioned" or "quaint" touch to it ...

With some nouns, both forms exist with different connotations:

e.g. "Fräulein" (outdated / non-pc term for an unmarried woman; sometimes still used as an address for waitresses)

vs. "Frauchen" (female owner of a dog or some other pet - "Komm zu Frauchen" - sometimes also used for "cute" women) ...

"-el" does not really exist as such; in Bavaria and Austria, for instance, it's more like a simple "-l" attached to the noun; in Swabian it's "-le", and the Swiss use "-li" ...