Yeah, too many good peppers to choose just one. That is very true!!!
I forgot another favorite annum. Also, it is landrace from where I live, the Canary Islands.
It's "Pimienta de la puta la madre" (Mother Whore Pepper). Incredibly sweet, tasty, like a candy. The heat is variable, some hot like a Jalapeño pepper, others like a Serrano pepper. The plant is also very productive.
Semillas.de has seeds for sale on their website (for the European people: last year I put a good handful of these seeds in the European seed train)
My personal favorite for flavor is the humble poblano with its mild heat and great flavor that virtually anyone can eat and enjoy. That is why the poblano features in so many of my hybrids. Next in line is the common jalapeno. There is a reason, in my mind at least, that those two are some of the most common peppers found.
With that being said, I also love diversity... but you asked for favorite annuum and for me it is the poblano.