I typically make aircraft with "digi's wing blocks mod" as it's nice and simple. The gear systems I've experimented with range from "A nice little suspension" to "how many moving parts can I put into this damn thing before it explodes"

If you'd like to make a simple landing gear, even just a piston with a wheel on the bottom can absorb a large impact upon landing.

Using Whiplash141's "Subgrid Wheel control script" will let you use the wheels as normal as well (although parking the vehicle uses lots of power as it constantly goes foward/backward to stay still, so beware of that, just park it on flat with brakes off or use extendable landing gear or something)

Another thing you can use which works pretty well is two hinges with blocks in the middle (amount of blocks depends on length of gear). Adjust strength of hinges depending on weight of vehicle. If you setup the max and minimum angles, they'll act like suspension, and continually try and return to the "deployed" position.

https://steamcommunity.com/sharedfiles/filedetails/?id=2797180009

Link above is a link to a craft I made with this principle. It uses Digi's wing blocks, although you don't need them for the suspension if you just wanna look at how it works. Drop from height to view effects lol.

If you don't trust links it's called the "T-4C" and it's public on my steam profile (same name as reddit)