I use AeroShell 15W-50. It's expensive but trivial on the cost of flying - about £60 for the 50hr service.
I did a number of alternates with Exxon Elite and the oil analysis never showed any pattern, so I think the two are equivalent as far as straight wear is concerned. Now I just use Shell because it is a bit easier to get where I am.
The fuel injected engine starts immediately, every time, from any "cold" temperature. Hot starts are a different matter (as any FI owner knows) but with a powerful starter motor it is sorted anyway.
There is a separate issue here in the UK, caused by most school/club billing being WET and charged brakes-off to brakes-on. So renters do as much as they can before letting go of the brakes. They start the engine and do the engine tests as soon as they reach them on the checklist, while it is still cold (there is usually no properly working engine oil temperature gauge anyway) then they race like crazy to the runway... I see this all the time.