Is there any difference between Warm regards and Best regards?
Regards is a synonym for greetings. Either phrase would be used in a formal letter; you wouldn't use these greetings in a letter to a close friend or family member. Warm sounds a bit warmer than best, but basically the two are interchangeable.
"Warmest regards" I use for close friends and relatives.
I wouldn't use "regards" in any form for close friends or family - it sounds way too formal. However, "regards" on its own in an email is fine for someone I don't know, yet I am having an informal conversation with e.g., admin for the house, kids etc. It sounds friendly, yet not too personal.
Best to use "Yours sincerely" for initial correspondence with business people. "Yours faithfully" is a bit old school.
According to the Oxford English Dictionary regards as a valediction literally means “best wishes,” therefore writing “best regards” is redundant. Avoid using it altogether. “Warm regards” and “Kind regards” were both created specifically to avoid this misusage. Both should be used only with close friends or colleagues.
To the extent there is no real meaning attached to it, best regards means something like, I wish you well. However, when used as closing ; Warm regards and Best regards don't have much real meaning attached to them and are just polite ways to end a letter. In that way, they are much the same as sincerely.But for the opinion, I would say it's better to use "Best Regards" instead of Warm or warmest.
One more thing, it's a reply to a specific comment here. "A letter from India signed "Your humble and obedient servant" or something"
Ans- Yes I saw and I know why they use that form of salutation. It's a British form of saying a farewell, a valediction. It's a formal Victorian format that maintained by the British in that era when India was ruled by them and as a consequence Indian people grasp the same form. I wouldn't say to abandon a wonderfully rich language but I do however suggest to use an appropriate (i.e contemporary) form that your reader will easily understand because a writing to prospects and customers aim for readability not a literary prize or award for Victorian prose.