Utila is better than Roatan but as RTBDiver says chances are slim. If one is spotted off Utila, most of the captains get the word quickly. A couple years ago - IDK about this year - at least one was spotted every month. Steve Fox who owns/runs Deep Blue is an ardent Whale Shark advocate - he works with the Shark Research Institute and Ecocean Whale Shark database people among others. My avatar is from there.
It's too bad you can't go in spring, that's the optimum time for them. They bring in specialists to lecture at night and actively look for whale sharks while you're diving. Capt. Swin has a reputation for finding them when others can't also - he did for us more than once.
Laguna Beach has a nicer beach than Deep Blue. The DB beach itself is ok but there's reef right offshore so no swimming. You can shore dive there, you enter over some rocks and swim out thru a break in the reef - the site is called Pretty Bush. Laguna Beach is on a dive site also and they have a dock to get you out a little deeper. The Labrynth site is near there also. Nobody does more than one afternoon dive and Deep Blue counts their two night dives as your 3rd dive of the day. We didn't see Laguna's boats go out in the afternoons either except ferrying guests to town so I'm guessing they're similar. As far as boat stability for your wife, Laguna Beach has a couple large Newton dive boats - probably the ones with the stabilizers.
If it matters, only Laguna Beach has a pool. We liked Deep Blue, the people are great, the food was very good, you get several choices at every meal and it was very quiet at night. The dive staff are all really fun also.
IDK Turquoise Bay but if a beach is a priority, and you're willing to have less of a chance to see Whalesharks, West Bay on Roatan is supposed to be one of the nicest beaches in the Caribbean.
Any beach on either island has sand flies also. Deet worked pretty well for us...I seemed to do better on Roatan than Utila but I forgot the Deet once or twice on Utila - going out at dusk on the night dives without it wasn't a good idea - both their and Laguna Beach's docks are on a mangrove lagoon - you could see the sand flies swarm in the sunset.
I doubt you'll see anything near Hamanasi in fall. I don't even think they'll bother to make the run down to Gladden Spit in Sep/Oct. They're only seen there four full moons in late spring/summer after the Cubera Snapper spawn - usually a month or so after they leave Utila - I'm guessing it's the same ones on their way to Holbox. It's a long way from Hamanasi and you really only go there to see the sharks, it's bland blue water diving otherwise. My friends saw a couple there last May a few days after the full moon. Splash Divers has details on their website. It's a long run down there from either Hamanasi or Placencia where Splash is located - a couple hours by boat.
