I've got a wishbone in mine. I've run the suspension through & past it's travel range. The wishbone joints are in the same plane as the 4 link joints so there's little or no movement of the slip joint. I went with a wishbone because I've heard bad things about diagonals, go figure.
If you look at the pic. of mine (pay no attention to the surface rust
) a diagonal would be at a pretty bad angle to stop lateral movement. I was afraid at that angel there would be too much stress on a diagonal bar.
Yours may work out different, I don't have much room between the tires.
Anything, especially if it's put together with heim joints will need pretty regular maintenance to be safe.
Just my opinion. Ask 6 people, probably get 6 different answers
If you have the room, a watts link is a slick set-up.
I should mention, I plan to pack mine with wheel bearing grease. I built it with an aluminum cap (slip joint end - see in pic) machined to accept a pressed in seal to keep the junk out. The other cap on the front end is just a dust cover. I'm sort of annal about details that no one will ever see.
15th Annual DRAGLIST Nationals Sometime in 2020. Somewhere in the USA.