The best texts omit but; so that the two clauses illustrate John's characteristic parallelism, and bring out the sharp contrast between the Baptist and his successor.
Among you (μεÌσος ὑμῶν)
The Greek idiom is a mid one in respect of you. Ἑγὼ, I, and μεÌσος, a mid one, stand respectively at the head of the parallel clauses, thus emphasizing the two contrasted parties.
Standeth (ἑÌστηκεν)
The best texts read στηÌκει, a verb which is kindred to ἑÌστηκεν, but with the added sense of firm, persistent standing. Thus, stand fast (1Co 16:13; Gal 5:1 : Phi 1:27). The verb emphasizes the firm, dignified attitude of Christ.