JFET amp in a pedal clues, please...

[Kinki fuzz]

I'm going to start to work in some crazy ideas I have and see what happens, but before I need some of your wisdom, I'm a complete illiterate on this .

If you were to work in an amp-in-a-pedal style project, based on a tube preamp or similar, what is the criteria for transistor election?. Usual approach is 2N5457 or J201 JFETS, but is there any reason for that? Of course there is... so, what is the reason for using one or the other? Depends on the tubes you are going to "simulate"? depends on the kind of preamp clean/crunch vs distortion? The kind of distortion, maybe? Am I freaking out? maybe just pop in whatever I have in hand and see what happens. ...I will probably do that anyhow but just want have some ideas not to work completely blind.

Thanks by the way to all of you for inspiring me back to pedal building.