Current visa start date - which one is it?

Hi, this might be trivial but I just wanted to check. I am switching to a Tier 2 and it asks what my current visa is and what is the start date. The exact wording is:

"What is the start date of your current visa or leave to remain?"

I had an entry clearance stamp on my passport which was valid from 24/04/17.
My original BRP has date of issue 10/04/17 (I lost this card last year and hence cannot provide it.)
My current BRP has date of issue 01/03/2018 (this is still the same visa, different BRP card).

Which one do you think is the correct date? I initally put 24/04/2017 but now am not sure.

Initial tier 4 visa.

Hi CR001, thanks for the response. When you say the initial visa do you mean the BRP card or the vignette on the passport?

Initial visa granted. Your brp replacement was only a replacement, not a change in visa valid to and from dates.