What do you use?

I've been using one of these for the last year.

http://www.masterlock.com/cgi-bin/product_detail.pl?dir=/automotive/towing/&product_number=374&numbersearch.x=15&numbersearch.y=10&sub_cat_id=D374&template=app

I can't say that I'm very pleased with it.  Chrome-plated and it has rusted to high heaven.  I spent 30 minutes earlier this evening trying to get it freed up and unlocked.

I'd really like to have something stainless as I'll be changing hitches quite often this summer (use different hitches for boat and camper).

Just wish I trusted people enough to go with a non-locking pin.

The hitch pin I use has a loop in it to use a regular pad lock. It was only $5 at lowes and it can use any pad lock. Work very well.

I have been using one made by Trimax. The set came with the receiver and coupler locks. It is the Epoxy one and havent had much trouble with rust so far.

http://www.trimaxlocks.com/rvmarine.htm

For as many years as I can remember I've use the fancy ones, the one with a hairpin clip or a bolt and nut.  Right now I have the hair pin clip on my pickup and a grade 8 bolt with self locking on my van.

Mine is masterlock item nuber 1480DAT.  Its very similar to yours.

No problems with rust thus far. Doesnt feel like it locks solidly, but never any problems!