I heard an improvement between the mk2 and the mk3 but I have no actual experience with the mk1.

Never compared it to an mk2 or mk3, but I like the sound on my mk1 and it was plenty loud enough for an event.

i only use pc. how much better is the soundcard? worth an extra $150-200?

It will still work with a windows 10 machine but not with a Mac OS newer than Mojave. It is compatible with Traktor pro 2 and 3.
The mk2 soundcard is much more improved though and it will work with all OS so it’s the better buy.

like if i played an event with a MK1 it would be suitable and the crowd wouldnt notice much? it would still bump?

I still rock my mk1. The mk2 is louder, I’m not sure I’ve ever seen measurable evidence that the sound card is objectively better in terms of SNR, distortion etc.

It’s certainly good enough for casual pro work.

kinda unrelated but had a chance to use rekordbox and ddj 1000 combo was way too intuitive, setup played like butter. haven’t had a chance to play with mk3 but now mk2 feels ancient. to each his own tho.
Edit: It gets the job done with a bit of hassle, I just feel like I could be doing more.

what do u mean? using old gear wasnt good?

S4mkii user here. just test out other stuff. you ll see what you could be doing. Sadly I feel like I lost so much time using old gear. maybe u diff.

I am considering getting a used MK1 over buying a used MK2 - 4 

does it still work with traktor and everything? or is it outdated?

Does the native instruments traktor kontrol s4 MK1 work with modern day Traktor/PCs? Or is it outdated?