ras mohamed is a daily accessible trip, thistlegorm needs the boat to leave the jetty @ 5 am and you are back 5-7 pm something like that... check crowly's blog he has detailed description how it goes.
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Both are nice.... Sharm is boat dives and no shore... Marsa is A mix between shore on the house reef, truck/shore nearby and some boat dives
For bus routes .... Well nothing is impossible but it would be something like 14-18 hours ride !!!! You can better get a flight sharm to hurghada (about 40 minutes) then get a shuttle to marsa (better to be prepared by where you are staying in marsa)
There is one specialist company that leaves later because they have a big, fast boat...
Used to be there but not anymore
few months ago i had to head from hurghada to sharm and desperately searched for this ferry then i had to drive my way.... Almost 10 hours with 30 minutes of rest !
A flight woud be the best option, just search for egyptair direct flights between sharm and hurghada... Avoid any flight with a stop