I'd have to say the Bersa .380 is the easiest I've seen.
Easiest = Bersa .380/9mm
Hardest = Ruger 22/45 (yuck...)
One doesn't even have to pull back the slide on those, right? Flip the switch down, pull slide off? Been a while since I had mine...
My sigs are the easiest.
Sig P220 is the easiest gun for me to take down
Sigs.
For easiest, gotta be the sigs. pull the slide back and lock it, drop mag, grab the slide with your left hand and push the locking lever down with your thumb, release slide, and it comes off, and you're done.
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This..
The 380 even more so than the 9, but both are easy. The 380s fixed barrel makes it a tad easier than the 9.
Funny, but I've always thought it the opposite. I've both the Bersa 380 and 9mm too and always liked the 9 take down a bit more than the 380. With the 9, you just drop the lever and pull the slide off. With the 380, you have to pull the slide back a bit to pull it off. Both are extremely easy, but I've always thought the 9 was a bit more fool proof.