Amigos are friendly and have a professional feel to them. They tend to have full boats which is something I personally avoid. Whern I say "full" I mean maybe ten clients which is not excessive and they will break into two groups for diving.
Local dives can be had without a pre-book. day trips might be harder. However, I'd bet a Belikin from Estel's that with one day's notice (12 hours) you can book any trip by walking up to an operator.
There are many good operators. I ended up using Aqua Dives: great boats and not crowded. They took great care of beginners and were aware of what people were up to.
I did Amigos for a night dive. Everything went well great but it was a little crouded with ten clients and two Amigos. Waiting for all those people to get on the boat while fighting a current was tiring. But, they are a nice operator and well equiped.