All of the Renderman-compliant renderers have pros & cons… (usually price vs. polish vs. integration). There’s no one right answer… but honestly to get your hands really dirty with the RSL/RIB workflow, grab the demo of Renderman for Maya as well as the 2-node free version of 3Delight.
The real power behind all of those renderers comes in the ability to programmatically manipulate RSL (the shader language) and RIB (scene files) before they’re written… if you’re really interested in learning the ropes, and have a technical bent, go for it.
The low-end version of Renderman for Maya is really meant to be a turnkey click render kinda deal. There’s minimal places where you can really hook into the real power underneath it (only really via brickmaps and compiling your own RSL).
3DL allows you to get your hands dirty with all facets (and it’s a hell of a learning curve), but the Maya integration isn’t as slick (it’s solid, but the workflow is kinda bolted on). 3DL also approximates a good amount of Mental Ray shaders for you… with Renderman if you want skin or arch mats, you’re going to be compiling someone else’s code at first or reverse engineering the 3DL shaders (that’s also the case with Renderman Studio/RFM Pro).
Anyhow, I’d say get both, but if you’re technically savvy and can code a little, focus on 3DL just to learn how RIB/RSL works under the hood. If you just want a different renderer to drop in with a different look than Maya Software/MR, focus on RFM.
Once you get used to the workflow and how each works within Maya, make up your own mind based on your taste. There’s no right answer
I’ve got Renderman Studio as well as 3DL, personally, and am digging into both of them pretty hard to get a grip on feature pipeline shading/lighting currently.