I rememberback in the day "teflon" seals seemed to be a hot ticket.
Wondering what is the way to go nowadays.

I'd say the common black unbrella ones are fine (bigger ones on the intakes for more shielding). the PC teflon types that require machining the guide top might not allow enough oil in in a DD but'd be the ticket for a dragger. #1 I'd want the stem clearance to be dead on (you're rebuilding I am assuming)

You will certainly want to stay away from Teflon valve seals. They will restrict too much oil when your stem to guide clearances are new and tight causing accelerated guide wear. Teflon also has "amnesia" and will not stay in constant contact with the valve stem.

A rubber seal is flexible and will always stay in contact with the valve stem however, it's lifespan is determined by it's chemical makeup to keep it from the "fully cured" state. Generally the most common quality rubber used for valve seals is a Fluoroelastomer, AKA; Viton, Fluorel, FKM, Fluorocarbon or what we refer to as Fluoro-Polymer. There are many different "blends" of the aforementioned polymer's.

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The newer umbrella seals seem to be made from silicone...takes the heat better.