water-shedding-est material?

why? Hot PTFE. :P (Leidenfrost shield)

Yes.

-CF2-CF3 ended surface is much less wettable than -CF2- (PTFE). Solid surface tensions are approximately 6 mN/m for -CF2-CF3, compared with nearly 14 mN/m for -CF2-. Note that interestingly, -CH2-CF3 has a surface tension even higher than -CF2-, so you really need that inductive effect.

You can approach achieving a -CF2-CF3 terminated surface with perfluorinated alkyl chains in place of methyl groups in PDME. Even better, oriented self-assembled monolayers (I could get non-nanostructured surfaces with water contact angles of over 170 degrees)

-SF6 termination is probably even better than -CF2-CF3, but a little too exotic at the moment...

As far as PTFE goes, go for full fluorination. Wettability drastically increases with each F that you replace with an H.

Also, aside from chemical property, if you introduce a heavily nanostructured surface with lots of capillary pores and as little true surface area comprising your macroscopic surface area as possible, you will get a very nonwetting surface, far moreso than by any chemical means. To see this for yourself, take your finger and place a small drop of water on the underside of a collard green leaf (I guarantee you it's not perfluorinated). Gore-Tex fabric incorporates a combination of these properties - capillary pores + fluorination.

suggested vendors, Sir?

Here's some more information:

Siltech makes various fluorinated silicone resins. PTFE is a no-brainer. FEP and PFA, are also sold under the name "Teflon", but aren't quite PTFE, to my knowledge. ETFE is sold as "Tefzel", PVDF as "Kynar", copolymers of various fluorinated junk "Viton".

Perfluorinated organosilanes and thiols have to be purchased from a chemical supplier (eg. Lancaster Synthesis). I saw a synthesis for alkyl-SF6 terminated organosilane in a journal article only.