What type of plants would work best?

The only thing I have found that will kill poison oak (which is what we have in the NWest) is a product called "Crossbow". It is expensive - about $30 a quart concentrate - & found at farm & garden type stores. It only takes 3 oz. to 1 gallon of spray, so it will last a long time. Some have used Roundup with good luck...but not me. Nothing "chokes" it out. I have seen 6 foot poison oak plants growing in the middle of a camellia bush. Be sure to cover up well, cover arms & legs & wear tall rubber boots if you have them. The resin can be removed with a product called Tecnu (available at most big box stores in the pharmacy section). Disinfect your garden tools with mineral spirits.

You won't be successful spraying the whole plant as is you'll need to cut it back.

Chop the poison ivy 3'' above the ground ..As soon as the vine makes new green growth spray with weed killer...It takes around 3 tries at getting, all of it..."round-up".."2 4 D"

i honestly don't think there's anything out there to choke it out. have you tried ortho's weed be gone max? you could also call your state extension agent and get his suggestions. GOOD LUCK!