Which valve spring tester do you guys have and use? Looking at getting one even though it'll probably only get used once every few years figure it'd be nice tool to have.

LSM

https://lsmproducts.com/

This

Bench type with as much open pressure as you think you will ever need
I broke, wore out an older model bench type mechanical tester that measure from 0 to 1000 Lb. on a gauge mounted on the front where it was easy to see ,
My new Intercomp brand is digital and will read from 0 to 1400 Lb.
I'm sure Al is talking about one that will measure the pressure with the heads on a motor at the races

The Rimac bench-mount testers were the standard, maybe still are. Kinda spendy but excellent.
Buddy of mine makes the smaller ones you use in a vise - Jeg's # 80538 is onet - and they also work great, calibrated on his Rimac.
Last I heard, he made them in 300, 600 and 1,000-pound maximums.
Usually $70-$80 depending on the retailer.

I use a moroso beam style when checking on the car. It works best to use as a comparison checker. I also have a bench style from comp cams.

I bought this one I found on Moparts many many years ago

I brought this one a few years back. It's great, don't take up much room & easy to use.

Me too.