Go with your gut, there is no right answer. I started my first draft from a middle chapter (it was unplanned. I was like "oh I wanna write this scene... and then... 40,000 words later....). It was a rough draft, I knew it would need work but once I finished from middle to almost end (ending was undecided at the time) I decided to go back and write the first draft of the beginning to middle.

Let me just say, I do not regret what I did. But I will say that by about chapter 4, I knew everything from middle to almost end would be rewritten. Most of the dialogue stayed, but settings were changed, side characters were changed / deleted, scenes & reveals were rearranged. But I just went with it because it felt right. By the time it was all written and rewritten, I have a second draft that honestly feels up to par with previous manuscript did at the fourth draft level. All of this (first draft to second draft completion) took about three months so it didn't slow me down. I just went with the flow, and paused to brain storm & outline as needed.