All lgbt flags are terrible because they don't follow the rules of tincture. /s
But seriously though, I think the trans flag is good. It has a nice amount of contrast and the colours compliment each other well. Other flags seem to have the problem of not enough contrast (like the bi flag) are too noisy (the main rainbow one) or the colours don't mesh well together (polyamorous). All my personal subjective opinion though!
Although it could just be because I've seen the trans flag a lot more than the others (which is fair; trans rights are super important right now).