Sorry for coming so late to the party
OK it depends on the amount of money you want to spend AND your patience...
For something truly superb: Declaration...well technically you can't buy a knot, but Scott will make you a knot for your brush handle - and I really love mine. You don't have much choice, but that's sometimes not a bad thing
If you know what you want - Bernd from Shavemac is your man. And forget what he has on offer on the site, you can Email him and pretty much get anything you want - dense/sparse, long white tips...only your imagination is the limit here I think. Not cheap, but don't forget you get 19% tax discount. And again, as far as I know, the only truly customisable knot on the market
I have an Envy White and while I like it, for me personally the Elite knot I have in my Platypus from Bob is absolute fantastic and I rate it higher than my Envy: super hooked tips, superb face feel...
Maseto on Ebay: solid knot, VERY well priced - I have a 50$ 30+mm brush that is really nice and super dense - my first brush from him shed and he replaced it straight away, no questions asked. I don't know, if he actually makes the knots himself, but he has definitely a very close relationship to the knot makers...
The problem with re-sellers (Elite, Envy, TGN,...): there is a sometimes huge variation between batches. I heard from someone, that 1 in 4-5 TGN knots are truly superb - but which one will you get?
Thanks
@alfredus for some good advice and interesting options. I think you are right about making sure I get a decent knot if I'm going to get a custom handle. As you and others have said it all depends on how much I want to spend, I'm going to have to look into the options and think about that.
And also think about the warranty: I am not sure, how much your handle costs, but I would assume you don't get much (if any) change from 100$ - and then imagine you have a knot that sheds in there. Or one that is scritchy (heard that about TGN as well) - or one that sheds AND is scritchy.
Getting a custom handle and a knot from separate places does have some risks involved, I would definitely only buy from a reputable and consistent source...
One more option you might have: if you already have a brush with a knot you love and a handle that you don't - get your handle maker to remove the knot (handle will most like not survive the process) and set that knot your handle.