POR15 would be my pic. I know some like other paints, but POR15 has always done well for me.
One trick I learned is to spray it with a top coat while it is sticky. But, spraying black paint, of any sheen, on black POR is difficult 'cause you can't tell what you've sprayed. So I've started using the silver color POR15 and hitting it with a chassis black spray. Lots easier to tell where you've been.
However, my shop crane, engine stand, and several other things are painted with the base black POR15 and they have held up really well to all sorts of abuse. So I'm pleased with the stuff.
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI