Is there any brand of valve stem seal clearly superior to others?

No real need to head for the highest-dollar alternative in Valve Stem Seals. Anything of OEM quality will be fine.

As mentioned, if the valve guide/stem clearance is still toward the bottom end of the clearance spec, the "deflector" orientation of the umbrella asals works just fine AND was recommended by my late machine shop operative. Consider that even the Chevy o-ring seal is probably the least expensive seal as it only seals when the valve is at max lift and port flow is at its highest.

When we were discussing these things decades ago, I asked about the PC-style seal as it had been purported to be "the best" in a race engine build back in the later 1960s. His reply was that as they scraped the stem of oil, very little oil would get into the guide, which meant "less lubrication" and "more guide wear", which is not good or desired in a non-race motor that we would like to see go 80+K miles between valve jobs.

Here's a long-term recommendation/source for B or RB gaskets/seals. Mopar Performance used to sell an "Engine Tear Down" gasket set. The advertised orientation was that it could be used for those "class winner teardowns" at high level drag racing events, where the winner has to expose what's in their engine in order to validate the legallity of their engine. It included everything from head gaskets to an oil pump pickup tube gasket. Back then, it was about $100.00 USD. I was not expecting much, but it had every gasekt to rebuild the motor. Even with, back then, steel head gaskets.

I seem to recall that 454 Chevy valve stems are the same diameter as B/RB valve stems and also came in a red/orange silicone for some applications. My machine shop guy would trim their length with a sharp razor blade for Chrysler B/RB heads. To me, THAT would be the only upgrade I would consider and they were OEM, too, which might decrease the cost a bit.

If the guide wear is where the oil is coming from, the silicone might be a bit more fogiving as the stem moves laterlally within its casting, possibly?

As for changing, you'll need a hand-tightened valve spring compressor to compress the valve spring and remove the two locks on the retainer. Once those things are done, then other methods can help keep the valve stem up (compressed air in the cylinder or other mechanical means) to lightly oil the seal/stem for installation. Then re-install the spriing, retainer, and locks. Being careful to get the locks back in their grooves on the valve stem fully before releasing tension on the valve spring. Might take a few times to get things to work smoothly?

Be sure to protect the upper fenders and anodized aluminum trim! Might be best to use a bore scope to inspect the cylinders to look for oil-washed areas on the piston tops, for good measure.

Most oil at start-up, especially overnight, might well be from valve stem/guide areas. In the middle 1970s, some OEM engines did not use seals on the exhaust valves, so they always smoked for a few seconds upon startup after they got some miles on them. IF that might help explain or justify things?

Just my thoughts (and those of my late machine shop operative/mentor) and observations,
CBODY67