Assuming tasers are effective, do US police forces carry them? If they do, why is it not the first choice? If they don't carry, what's the problem with tasers?

Assuming tasers are effective, do US police forces carry them? If they do, why is it not the first choice? If they don't carry, what's the problem with tasers? If tasers are not effective, I'm still wondering why non-lethal weapons do not seem to be the first choice. Would all known non-lethal restraining tools be inefficient (too slow) if we assume the civilian will make use of a firearm? I mean, let's say tasers are not good enough, maybe pepper spray or something else can be used. Genuinely curious and probably missing important details.