İn my view it is perfectly reasonable, in today's world, to address your pilot colleagues by their first name within the confines of the company, however, the exception to that is when you are on board an aircraft and/or are in earshot of your passengers, then rank and surname should be used. İt is an important safety consideration that passengers understand who is in command and the use of the title 'Captain' or First Officer re-enforces that, you never know when people will need act directly to a crew command for their own benefit and no doubt should exist as to who's in charge or second in charge. Same applies in the cabin of course with respect to the SCCM.
There is however, another argument for addressing the commander as Captain, and that's business courtesy e.g. when a handling agent is dealing with foreign carriers as their customers. Often in other lands a greater degree of formality is likely to exist and if you want a good journey log report on how well you handled their flight then it doesn't cost much to be that bit more formal. Just think of it in the same way as a shop owner will often refer to you as Sir or Madam.
On occassion, and in my 35 years in this businesss they have been few and far between, there are those pilots who demand respect and the use of the title Captain, very simple to deal with- you simply request that they address you as 'Mister/Miss/Mrs.', soon balances the tables.