Shimano = smooth and quiet (I call it vague and deceiving)

SRAM = sharp and loud (I call it precise and ensuring)

I prefer the confidence you feel when shifting with a SRAM-equipped bike. Once you hear that positive rear shift happen, it means you're locked in and good to go.

Shimano, OTOH, makes you think you're in the next gear, when really you might not fully be and then once you mash down on the pedals you get slippage. Slippage = not cool. Sometimes it's also hard to even tell if a down-shift (to a larger cog) even happened. Some people prefer how "smooth" Shimano shifting is, but IMO it's not a good thing.

But, as others have said, you need to go try them both and decide for yourself. Good luck!