For a spouse of US Citizen, sponsoring as a spouse is the best route and K1 is not recommended as you are already married. Also, it saves you money in long run because K1 visa holders need to adjust here whereas spouse of a citizen come as a green card holder. Time wise Spousal petition might be just a couple of month longer.

Bandita Sharma Dahal, Esq.
www.philadelphiaimmigration.co