"Improviser" or "improvisor"?

I'm trying to determine whether I should use the ~er suffix or the ~or suffix for a person who improvises. What I've learned on the web is that technically one should say "improvisor". The ~or suffix is for words of Latin origin, and apparently the word "improvisation" derives from the Latin improvidus.

However, "improviser" seems to be the more common of the two, and I have to admit, it feels more natural to me.

I've been using both, but I want to be consistent and settle on one.

Which one should I commit to using, and why?

Well, then English must feel more natural to you than Latin. The usual English agentive suffix spelling is -er, now pronounced /-ər/.

Improvise and improvisor, on the other hand, come originally from Latin im + prō + vīsus '(something) unforeseen' [English un + for(e) + seen -- the prefixes are blatantly cognate], and imprōvīsor is simply a regular Latin agentive form. With an -or. Which would have been pronounced by ancient Latin speakers, along with every other letter in the word; Latin spelling represents actual pronunciation (circa 0 CE); in this case it'd be pronounced [impro:'wi:sor].

Doesn't sound or look wright to me either.

Oh, and as for advice on which one you should commit to -- do what you please; that's what everybody else does. After all, it's your language, and your spelling.

The advice you got on the web is worthless. There is no rule. Use whichever you are happier with - probably the more common, unless you want to be different.

It took me a long time before I got it into my head that when W.S.Gilbert wrote The Sorcerer in 1877, he spelt it that way, and not "The Sorceror", which I believed was "correct".