knoxb
I've got 3 of the 4 you mention, and 1 you didn't (Warhammer). I didn't purchase the WE fret because having the other 4, there wasn't much I didn't have. Personally, I do think you need more than just one. For instance, the inspection hatches and air balast vents on the saddle tanks only appear on Jason's Modlebrass fret. Detail for the top of the UZO, and sky periscope shears are on the Yankee Model Works fret. And by far the most detailed, IMHO, fret is Eduard.
The Warhammer set includes such detail as arming props for the torpedos, the heads of which are molded into the forward torpedo room replacement bulkhead, the attackscope guard which mounts on the shear, the conning instrument panel with compass and engineroom repeater, solid metal lookout steps for the walls of the conning tower, etc.
You mention that you're not considering the decking, but if you take a close look at the Nautilus deck, which I am also using, you'll find detail such as the anti skid plates, access hatch hinges, and other details are scribed, but not really raised. Eduard's fret has over 60 small hinges for the access hatches alone. Also, the small access hatches which are molded in the upper and lower conning tower are provided as separate units. Backing plates for the conning tower handrailings are included in both Eduards and YMW.
As for the Warhammer set, the main reason I picked it up was for the replacement conning towers, the conning tower detail including shears, UZO, aiming binoculars, two compasses, and two resin periscopes. The PE parts come with the resin set.
K, it might be a good option to get additional opinions, but I don't regret picking up sets that I did, and used numerous parts from each.
Thom