I would try both, the install is very quick, skip the bitcoin node when you are testing it out, since that takes a long time to sync and there is no difference in the bitcoin experience between the two.

Where you will see the biggest difference is the amount of available apps, umbrel still has more. It depends which apps you need in the end.

Start9 has an integrated backup feature that umbrel lacks. So start9 might be a better choice for the file share server part...