Not all paint is created equal. Neither are all powdercoats created equal.
What kind of powdercoat failed on you? Was a cross-linking powder or a straight plastic powder? What kind of either? Of course, your powdercoater will not tell you. They will powdercoat with whatever they powdercoat everything with.
Paints: Polysiloxane, Siloxane, Long-chain Alkyd, Medium-chain Alkyd, Short-chain Alkyd, Acrylic polymer, Latex polymer, Single-component Urethane, Two-component Urethane, Single-component epoxy, Two-component epoxy. Novolac, polyamide, polyamine, phenolic, coal tar and water based epoxies.
What type of paint would you like to use? I'm assuming you want indestructible paint.
The stuff used on heavy construction equipment is 2 part polyamide epoxy. Usually brushed on to create an extremely thick coating, something like 4 or 5 mils.
If you really want an indestructible finish, hot dip galvanize with 2-part epoxy topcoat is best.