Thanks for all of you taking time to reply. I think there might be some misunderstanding: what I am concerned about is the difference in features between tuareg and caml-mode, not any questions about how to configure either of them.
I am a raw beginner at OCaml. For the time being, I have used opam to install and configure merlin as suggested in Get Up and Running with OCaml, and also (not covered there) used opam to install and configure tuareg. It seems to be working well.
A little earlier I had caml-mode but did not use it extensively. My crude impression is that editing with tuareg, the code looks prettier, but I could not tell what other differences there were. So if anyone with deeper knowledge of both tuareg and caml-mode wants to chime in, I will be eager to listen. If not, I will just continue with the setup I have for a while! 