Possibly looking into using IEMs in the future. Want to start researching some brands and what to go for in an IEM

So far everyone ive spoken to has said Sennheiser EW300 is the best out there.

Any other IEMs you guys had experience with or can recommend?

Problem is these things are really expensive at the level we need so I heavily want to research it
I've mostly used Shure systems, but we're often handed a pack and that's it.

More important to me are the earpieces, which are yours alone, personally molded (forget whatever comes with the setup). I think mine are Ultimate Ears. I recently tried an ACS system, which is able to add ambience to your mix. Lots of engineers have ambient microphones that add some of that to your mix, but there's often enough of a delay that it's not particularly helpful. Complete isolation takes some getting used to. ACS, however has some kind of a setup with microphones that allows you to hear a certain percentage of the stage noise closest to you, and that can be really helpful.

Be a bit careful with the Sennheisers if you're using the accompanying instrument bit; make sure that part works perfectly before you take it out. There have been some issues getting things to work together.