There was a thread for this, but it was back in 2015 so I wasn't sure if people would like me necroing it.
Behind Enemy Lines: Discret Explosion I guess, it's a fun little level. (I honestly barely remember most of the second half of Behind Enemy Lines, it's not bad but I think the limited mechanics of BEL means they all sorta blend together for me.)
Behind the Call of Duty: The Asphalt Jungle, the Zoo setting with hostile animals is pretty cool and unique.
Commandos 2: Saving Private Smith, I like the location of an town mid-battle, the Thief-only start is cool and requires more evading enemies than tying them up and the finale if you got the bonus books with the Invasion is a nice bonus.
Commandos 3: Protect O'Donnel, a nice change of pace with a defensive mission against the hordes of German Soldiers as you protect O'Donnel, you get to use the Assault Rifle and the Stalingrad setting is cool.
Commandos Strike Force: Cold Reception, one of the few levels where you use all 3 Commandos, (even if not together) it's the only level with the Shotgun and the only mission where you have the option of stealth with multiple Commandos with the Spy and Sniper in the second half of the mission.