Beds and reclining seats are a tiny bit more comfortable to sleep on than regular seats (4, as opposed to regular bed’s 3). Still less than “real” bed’s 5. This only affects difficulty of falling asleep.
Beds don’t count as seats, meaning you can’t drive from them (unless you use the remote vehicle controller).
Regular seats are more resistant than reclining ones (300 vs 100). And even than military ones (250).
Other than that it’s all about cargo.
There is no reason to use beds at the moment. Reclining seats may be better if you have problems sleeping, but otherwise it’s just seat vs. military seat.
There are also saddles and foldable seats. They’re nearly identical, except foldable seats can be installed anywhere (even in “stupid” places, like in the middle of an aisle) and use cheap sheets as material, while saddles are more resistant but require the center slot.
Wood seats are like military seats, except less resistant (125).