I don't use Nutmeg or Moneybox, so I can't provide any advice on them. I think @Steph10 has some experience with Nutmeg. She might be willing to share.
When choosing investment platforms, I look at three things:
- The range of investments available on the platform: I invest in global index funds, ETFs and US stocks.
- Fees: How expensive are they? I don't want to give half of my returns to an investment platform.
- Past performance: I know past performance is not a guide to future returns, but I will not put my money in a consistently underperforming fund.
I hope this is useful. Sorry I couldn't be of more help.