These days trombone players probably have a greater choice of instrument brands than any other brass band players, which is probably an advantage for us.
However, for any instrument, I would definately say try a few different makes before you buy, and choose a brand X instrument because it suits you and the way you play and because you get a good sound on it, rather than buying a brand Y instrument because it happens to be fashionable at the moment, or because brand Y is used by a famous player in a top name band.
Way back in the 1980s I was looking for a new bass trombone, and it came down to a choice between brand A, which was very popular and fashionable at the time (and is still popular today), and brand B, which at the time was not well known, at least in brass band circles (brand B became popular a few years later, but seems to have slipped back again these days. The vaguaries of fashion.). I tried both, but it only took a few minutes for me to discover that brand A was not for me, even though many fine players used it and sounded terrific on it, so I went for brand B instead, which suited me much better.
The instrument I play currently, while a well-known and established brand, is not particularly popular these days, at least in brass bands, but it works for me.