parking on hill

Grit dog wrote:
Good condition RxR ties will last a long time, but not as long as a keystone type block wall.

Consider this. An assumed 12x20 pad from 0-3' tall is about 13cy of fill material. Too much to unload and place by hand efficiently. So you'll need a machine and know how to run it., but only basic skill sif filling in behind a wall.
For a little over double the amount of material, if you have the room, you could build the same pad with 2:1 slopes and no wall. But requires more skill operating a machine, better compaction methods and future maint (mowing the slopes).
Probably a toss up, depending on material availability and your skills as an operator.

The wall will require grading each base lift run separately and accurately. With RxR ties, I'd consider battering the walls 1"-2" per row. I'd consider dead-manning a few ties into the fill, maybe 2 on each side about mid way up although if you build the "box" right, it will hold 3' of fill.
Fill material is dependent on your source. But best would be something more granular and not alot of fines and no clay.
Properly compacted. Still need to top with base course or gravel.
Or you could run dirt all the way up, 2 rows of pavers for wheel paths and plant it, but I'd rather have gravel underneath.

We leveled 14 tons of 1&2 rock and 7 tons of 57 rock with some shovels and rakes, 2 day job with 3 of us, a hell of a lot cheaper than renting a machine, and some manual labor once in a while is good for the soul and body. Now if you're to the point where the body is no longer done better by working then I understand where the economics might come out differently.