Deep Blue seems to be having difficulties lately - I hope they've turned it around though. This isn't exactly current (Dec. 2015) but mirrors some of what you can read on TripAdvisor (not my favorite source) also.
Seeking info on Deep Blue Utila
Steve was still in charge when I was there and they still had their own boat - and Capt. Swin who had a reputation as one of the best at finding Whalesharks. Since every boat legally can only make two drops per sighting, the other captains talk sightings on the VHF so they can all do better for their guests (and tips). I've read that Swin is no longer with Deep Blue and that their affiliated shop in town has closed also.
Shirley is very nice but she's in her mid-80's now and if she's running it all, I'd guess the problems could be true. I hope it's not since Laguna Beach just closed and being basically next door that should help drive traffic to Deep Blue. But IDK...
and a nice (upscale) resort
In it's prime that wasn't Deep Blue. It was nice enough but pretty basic before they started having difficulties. Everything is a little dated there - the furnishings, the lodge, slow wifi only in the lodge or the deck of the closest room (ours) but not inside. And the bugs at night made that not such a good idea. Nice view though, all the decks look out at the Pretty Bush divesite.
It seems like AI resorts on Utila are all suffering. Laguna Beach recently closed for good - all they're doing now is honoring existing reservations.
From a sand fly perspective, I'd pick Utopia also. I spent one afternoon barefoot on the beach at Deep Blue and collected a couple dozen bites on my legs - and I'm pretty serious about using Off with Deet. Later that week one night we left the patio door open - but screened - and woke at 2am to a bunch of mosquitoes buzzing around - turned on the fans and fogged the room with Deet. Also Deep Blues dock is on the Mangrove Lagoon and it's pretty still in their inlet - one dusk dive there was a huge swarm that attacked b4 we could get on the boat and out. Utopia being farther away from the Mangrove's should be less affected.
We were there during a Whale Shark Research week and our expert (Jen Schmidt) looked so bad (she went birdwatching in the lagoon one day) that we were kidding her that she'd be quarantined on arrival in the Phillipines - she was flying there direct.
Your timing is about right - ours was the last week of March into April. Snorkeled with at least 8 over two days then the weather turned flat calm - good for other diving but we only saw boils after that and one might've passed under the boat briefly. All were 16-20' males and once a big female - bigger than the boat. Did get to see vertical feeding by one of the males for several minutes - the rest seemed mostly disinterested or dove when we got close.
I haven't figured out what
research week means either - optimum sighting time or optimum for the resort or the experts travel schedule. But March-April are mentioned by other sources I've seen as the
best time for sightings.
hth,