I always use the checklist on the ground (and I still miss stuff, did a whole flight without the strobes on the other day, didn't realise until I came to switch them off......, which makes me think I should always carefully use a checklist and run my finger down each item. It's easy to get distracted by a passenger or radio call.) I fly four different types as well so I probably couldn't commit everything to memory even if I wanted to. Memory in the air although some non emergency failure stuff other than engine failure/fire I would have to get the checklist out.