What is the fastest to bring my fiance to the US from DR. Will it be faster to marry in DR or get a fiance visa and marry in the US?

So, there are two pathways to achieve your goal. You can either apply for a fiancée visa and then have your fiancé come to the United States and adjust status to get a green card, or you can get married first, and then apply for your Spouses spousal visa and your new spouse will process at the US consulate in the Dominican republic. The fiancée visa is taking slightly less time I would say a total of maybe 2 to 3 months less, but the process is still going to take a year.