I've taken the trip between Roatan and Utila several times now, and have utilized the 3 traditional ways of getting to/from.
As explained above there are the ferries. They are reliable. Pay the extra $7 for first class on the galaxy for the A/C if its hot out. From La Ceiba to Utila they are using the new(er) smaller boat, which I wasn't fond of. It gets you there and back, but it is not comfortable, you don't feel safe, and you are cooking inside the tin can. But for $60 you are from Roatan to Utila (or visa versa) in 3 hours. I will use these taxis again.
There is also Capt Vern with his daily trips direct betewen Utila (6am) and Roatan (1pm but will delay his Roatan departure if you ask). This trip is rouhgly 4.5 hours and $55. If you get sea sick take Dramamine early. I have never been sea sick in my life and I spend A Lot of time on the water and I got sea sick with Vern. It is slow going and rolls over the waves plus fumes from diesel fuel add to the noxious feeling. I doubt I personally will use Vern again unless I need to for scheduling conflicts.
I have also taken the island hopping plane. When I took it in 2007 the runway in Utila was gravel but I noticed last month is has been nicely paved now. I forget what I paid but it was at least twice the cost of the ferries, however it also took about 20 minutes. I'm not one for flying, however, so it is an interesting flight for those like me. Those small planes can get scary. I may use this service in the future, but the higher cost and my lack of flying will make the ferries my first choice.
If none of these work for you, there are several other options, but all of them start increasing in price substantially.
HTH