Personally I hate ATTN and TRAC. ridiculous rebate fees, and stops runs dead. thankgod LSPD is gonzo.
NX is a love/hate thing; that qualifies it as my 'most hated.' Too, it's not really an ECN at all, though it pretends to be. I think I hate it more for that, than anything else. But then again, it probably doesn't qualify as an ECN, so nevermind.