On occasions such as those when you don't care about the special properties of either single or double quotes, which is the best to use.
My hunch is that single would be better because there would be less processing of escaped characters.
On occasions where it doesn't matter whether you use double quotes or single quotes, there are no escaped characters, so no processing of escaped characters happens. If you mean looking for escaped characters, remember that with single quotes, the tokenizer still has to look for them, as the delimiters, and the escape character, still can be escaped.
As for which is the best, I'll tell you which is the best, if you can tell me the measurement you mean by "best". Single quotes use less ink when printed, perhaps that's a reason to find single quotes better. OTOH, a lot of printing software (specially printing software used in (bad) Perl books) mangle single quotes into something unrecognizable. Which would mean double quotes are better. Then there's C, which uses double quotes for strings, perhaps that makes double quotes better. But a double quote means I have to hit the shift key, but I don't need to for single quotes. Perhaps that makes single quotes better.
Oh well, perhaps we should reach the conclusion that "which is better" questions that don't come with a measurement are pointless.