I really like making and flying Falcon 9 style 1st stage booster rockets, though its kinda hard to adjust them for specific payloads. With a normal booster you can just slap a bunch more tanks or SRBs on it, but that would throw the balance of a F9 style stage off. Also I go full Falcon 9 in that I do a boostback to the KSC and land it propulsively- on the grass or on some poor KSC building
Here's a pic of my 2.5m and 3.75m boosters:
And yes, it does save some launch cost off of the payload. Its not really worth it with the light 2.5m booster, but I still do it cause its fun.
Regarding spaceships, I have yet to design a fully reusable transfer vehicle. The ships I use for my manned Duna and Eve missions are both single-use only, since they use chemical engines which means I need drop tanks to give them enough Dv. I also don't bother with designing special return capsules and landing them at the KSC like the Dragon V2 (though I might later on), I just slap on some parachutes on a 2.5m pod and land it somewhere in the ocean. I have experimented with reusable shuttles and made a rocket SSTO for tourist missions, but they don't save that much money off of launch cost, especially when using a space shuttle approach.
By the way, FMRS is a must-have for building and flying re-usable rockets. Though I'm not sure if its up to date with the newest version of KSP...