For the OP, which 20 specialties would you envision taking?
I find 31 national specialties. By 20, my rough grouping leaves you a sidemount advanced-rebreather altitude ice cavern wreck dry dpv diver. Which takes a broad dive environment. With a few fillers. If well taught you could learn a lot. Though a *good* intro to tech would likely make you more competent in the water than doing this slip shod. Or you get heavy into the environment and photography. I agree the dive count needs bumping up to match the onslaught of classes.
Nitrox
Nav
Night
Boat
Deep
Search and Recovery
Delay SMB
Peak Performance Buoyancy
Emergency O2
Multilevel diver (two and three level dives with eRDPML)
Drift
DPV
Sidemount
Cavern
Wreck
Dry
Ice
Altitude
Rebreather
Advanced Rebreather
FFM
Fish ID
Project Aware
AWARE Shark Conservation
Coral Reef Conservation
Dive Against Debris
Equipment Specialist
Underwater Naturalist
Underwater Photographer (Digital)
Underwater Videographer
Adaptive Techniques
I have the followong specialties:
Drysuit - it was good to try cold water diving to understand whether I will like it. Also, gor few specific skills required for drysuit diving.
Nitrox - is a must if you want to go to tech diving. Also, without this specialty you will not get nitrox fills.
Search and recobery - really liked it as I learned various search patterns, praftically tried recovery of various objects.
Deep - it was interesting to dive to 40 m depth and see how nitrogen narcosis could affect me. Basically did not learn anything new, however, some LOBs require this specialty if dive sites are deeper than 30m
Uw naturalist - useless waste of money
Drift - practically the same as above.
Wreck - learned some basic wreck diving protocols, however, for serious wreck diving a much rigorous training woild be required.
Night - night diving was interesting, however, from skills point of view, no additional skills learned.
From remaining and useful padi soecialties are Ice diving and DPV. Maybe will take them in a future foe the sake of fun. Remaining padi soecialties are useless for me or should be taken with other agencies (eg cavern, rebreather, sidemount)