I love Krabi, but depending on what you are looking for I would also suggest Koh Lanta (which you get to from Krabi airport - 3 hours and two ferries away). On Koh Lanta my favourite beach is Kantiang Bay, which is the home of one amazing 5-star resort (Pimalai) and some really cool smaller hotels and a bar. What is great about this beach is how few people there are, plus you can head out diving (depending on the month) from there too.
When will you be there?
Anyway, back to photography!
Of the lenses you mention, I would suggest you take these three:
Canon 17-40L F4
Canon 50mm F1.8 II
Have a safe and enjoyable trip, krub!