ADF is probably the most expensive hullmod for Paragon, aside from Heavy Armor (which I normally do not use, due to mobility malus). If I have ADF on it at nearly all times (and I frequently take long distances trip with one), it makes sense to s-mod that, which costs 40 OP, instead of something else that costs only 25 OP.
That said, in my last game, I only had a single s-mod on Paragon - Hardened Shields. I made do with ADF (paid 40 OP for it) and I had no other s-mods because I was hoarding story points for colony improvements (thanks 2^n costs). If I added a second s-mod on Paragon, it would have definitely been Augmented Drive Field for being the most expensive hullmod on the ship. Of course, I consider burn 20 a must, and I do not want to clog my fleet full of tugs. If I want to clog my fleet full of something, it would be Dooms (for maximum cheese) or Phantoms (for raiding power). Phantom is MVP this release because of its Advanced Support Package (if I have 200 marines per Phantom), good for stealing rare items or lots of vendor trash without the need to bring lots of marines.
Story points is the Vespene Gas of Starsector.
P.S. Main reason I did not double s-mod my ships was because I wanted to see if I really needed them. I was doing fine crushing named bounties flawlessly with phase fleet plus Radiant (or Paragon when raiding for blueprints because Ziggurat cannot stealth raid.) Only when I started fighting Ordos with multiple Radiants is when things got hard, but by then I did not play much longer (and I used Dooms to cheese the fights with Radiants.)