I've used both and am currently using the roller type clutch release bearing on my fairly close to stock MGA race car. I have the MGB pressure plate modification with the MGB front plate on the transmission, so I'm using the larger MGB sized throw out bearing.
When everything is really, really hot after a race, I can sometimes hear the bearing rollers rolling when in neutral. But a standard graphite throw out bearing may drag just the same under similar heat conditions. I think it's six of one, half a dozen of the other. I pull the engine fairly often and usually see one or two moderate chips out of the graphite but can't really see damage on the roller type throw out.
I think you are safe with either, so go with the cheapest and don't ride the clutch.