I am looking to replace some worn out bearings in a Shimano Hollowtech BB.
I am seeing 6805 bearings in: deep groove, full compliment (no cage,) angular contact,
ceramic ball,full ceramic, and silicon nitride ball.
I see open one seal (original equip style,) double seal, and double shield.

Which would be best?

I assume you are referring to a Hollowtech II (external bearing) bottom bracket, not the older Hollowtech (Octalink) style. Is that correct?

Are you planning to push out and replace the bearings in the old cups? Frankly, these bottom brackets are so inexpensive that replacing the entire thing makes more financial sense unless you think you are going to achieve some major increase in efficiency and cost isn't an issue. If that's the case, go all-out and get the full ceramic replacement bearings and hang the cost.

Thanks.
Yup. Hollowtech II outboard bearings.
Bearings have already been pressed out.
This is just an experiment. I'm just like that.........

I also see Phil Wood bearings available. They are s'posed to be good uns.

Yes, Phil Wood bearings are good and Chris King also sells replacement Hollowtech II bearings which are very high quality too. Either would be a good choice if their cost penalty isn't a consideration.

Even mediocre ball bearings, in good condition of course, are so efficient that you will probably need instruments to measure the improvement in going to the best ceramic ones.

Except for the cost and bragging rights, of course.

The seal drag is probably an order of magnitude higher than the drag of the bearings themselves.

Absolutely true but I wanted to avoid that discussion/argument.

I have never been dissatisfied with Phil bearings. Andy.

You could also try these guys. They make it easy for you. IMO go with the steel bearings for durability per dollar. https://www.enduroforkseals.com/id227.html

Their replacement bearings, particularly the steel ones, are reasonably priced but the installation tool set is very expensive for home use.

I suppose you could use the hammer and punch bearing removal and hammer and big socket replacement techniques but I'm not sure I'd want to do that.

Yeah new BB's aren't that expensive but the OP already has the old bearings out of the cups. Just throw the cups in some boiling water for about 10mins and put the new bearings in the freezer for a few hours beforehand and they go in without too much effort, no expensive tools needed.

Thanks y'all for the selection suggestions, the sources and techniques.
I'll figger out what I'm gonna do..........

Here's an interesting bit on BB friction measurements. Note the lowest friction bearings have no lube and seals that don't.

https://www.bikeradar.com/us/road/gea...et-drag-39233/