As others, I can't say they're the "best" but when I did a straw poll on Twitter a few years ago, I was recommended RapidSSL. I've used them on my own sites and for clients since then without any fuss (5 minutes and one automated call). They seem to be very one size fits all though, quick and easy, but nothing fancy like EV. (If anyone can help there actually, any recs for good but non-expensive EV providers?)