I have done a few trips to Bali. If my focus is diving; I'd base myself in Tulamben over Amed; although there are more and better restaurants along the Amed strip. I have not stayed or dived with Liberty Divers, but have heard good things said and would probably pick them if / when I get to go back. I have dived with Tulamben Wreck Divers who were fine, but make sure you are clear on your accommodation requirements because they have two sites, one of which is apparently nice, but not very conveniently located unless you have a scooter. I also like diving Nusa Lembongan, but I am told the island is getting pretty busy nowadays.