Been using IEM with my Axe for about 6 years as has our singer and guitarist. Just a footnote we play in a hybrid band to a partial back track on silent stage. I started with Westone 4R, from a Sweetwater recommendation, and it was a good sounding experience. One finally went out and we ordered the Shure SE215 in emergency. Comparitively they were good for just that. An emergency. The experience was lacking however they did have a surprising bass response.
With the 4R no longer available I called Westone. He said 'interesting... the 4R isn't a in ear monitor per se'. It's just a good set of earbuds. I recommend the 3 driver UM30 or AM30. UM = isolated, AM = Ambient. I asked even over the 5 driver UM50? He said 'yes in your situation and for guitarist' the 3 driver is recommended.
So I got the UM30 and they are very decent for the price. I keep them very clean with 'lens wipes' from Wally world to prevent what Chris mentions and replace the pad inserts pretty regularly. For the singer we ordered the ambient model (AM30) because she doesn't like the total isolated sound much. Personally I did not like them at all.
All of the above equations could drastically change in a 4 or 5 piece live band relying on stage sound for interaction. You might like the ambient model but for me the UM30 was a killer deal. FWIW I don't care what the guy says I'm going to get the UM50's to try out the 5-driver model...lol.