I'm seriously considering an HK USP 45. There are many variants though ...  which one to get?

These seem to be what I need (I'm right handed shooter):
- Variant 1 DA/SA with control lever (safety/decocking lever) on left
- Variant 3 DA/SA with control lever (decocking lever) on left

What's the difference between safety/decocker (varian 1) vs decocking lever (variant 3 only?

Thanks!

V1 you can carry cocked and locked, OR decock for a DA first shot
V3 is a decocker only (like a Sig P series P226/229/228/220) no safety so no cocked and locked SA first shot
V9 is a safety only, no decocking (cocked and locked only like a 1911, but you still would have a second strike DA pull if a round failed to fire)

ETA: I see no point in V3 unless you are LEO and MUST have DA first shot.  You get the same function with V1 and with V1 you get the option of the SA first shot cocked and locked if you want.  The downside is that if you ride the V1 safety you may accidentally decock, that's why I threw the V9 in there.  If you like the 1911 SA C&L, go for the V9, otherwise, V1 will work great for you I'm sure.

I would get Variant 9 and carry Condition 1. However the majority, including both of my dads, are Variant 1. I still use them in Condition 1.

I'm converting a couple of V1s to V9 as soon as I get the parts.  All of my USPs will be V9 going forward, though I'll likely have to buy them V1 and convert for obvious reasons.

Thanks for the info. Variant 1 is what I want.

it is the most common option.