Medic: (Not really play much with this class) Started off with the Cei-Rigotti Optical - You get a red dot sight but obtrusive sight holder, 10 rounds, not bad.
Support Started with Lewis Gun Suppressive with 97 rounds and a tripod, which was ok, especially shooting from prone. At the moment I'm loving the MG15 NA Storm, 100 rounds and quite accurate, although can overheat.
Assault The Automatico Storm or Trench(hipfire) is strong gun although the mag gets in the way, but I love the M97 Trench-Gun Backbored shotgun. It has a faster fire rate than the Model 10-A.
Medic: I've been mostly playing medic- found Cei-Rigotti < Mondragon < Selbstlader M1916. Symthic shows the Mondragon and Selbstlader have better damage profiles (-1 BTK), and the Selbstlader has a 26 round clip (compared to 10). Currently using the Selbstlader M1916 Marksman (strongly recommend). I've heard good things about the M1907 SL Sweeper, which would be a good CQC alternative to the Selbstlader M1916 Marksman.
As far as Medic-ing- would it be terrible if I swap out the Crate for the RPG? I will never not use the syringe, though.
Scout: I would get the Mars Automatic Pistol ASAP, and ditch the SMLE MKIII Marksman for the Russian 1895 Sniper right after that. The Russian actually has a decent scope. I've heard a lot of "Flare Gun OP" talk, but I honestly love the trench periscope. You can rock the leaderboard with 0 kills while giving your team wall hacks. I believe you do have the "sniper scope glint" while using it, and can be marked- but as long as you have good cover the enemy is just wasting ammo.
I want to try the M1903 Experimental as a CQC alternative, but being a semi-auto is a bummer (fancy mouse can fix that though). Not sure if it's worth picking up when the Mars Automatic Pistol kinda fills that role.
Support: Air Burst Mortar < HE Mortar. I had to swap out the normal sights on the Lewis Gun for the AA sights.
Assault: Shotguns. That is all.
Maybe use the Hellriegel 1915 Factory when you get tired of winning with shotguns, because you are already lvl 10 Assault class from using shotguns.