When I'm searching through the community I kind saw that FCEUX have horrible Input lags whic is pretty much bad at speedrunning the game if you're doing a sub 5. Is it really have a bad Input lag and What emulator that has no input lag (probably none because flat screen have input lag too). Probably not bad because blubbler [or i_o_l] got a wr using FCEUX.

Every emulator have input lag

Well I already think that every emulator have input lags (I saw a problem because I said none in probably none) But why everyone are using Nestopia in another reason? Maybe I'm blind about that.

Nestopia has minimal (unnoticable to me and many others), input lag whereas FCEUX has a noticeable input lag that is a bit longer than Nestopia's.

Nestopia also runs better for many, along with what @Tecate said.

Wow, I think I like to test out what Nestopia power was. Lolz. But it's my choice to choose what emulator I want to use and also I use FCEUX alot and I never notice some input lags, maybe some little. Well I'm still need to learn how to use it.