Is it always better to do a meter reading every month or an estimate?

I've done meter readings for ages. If you don't mind doing it... It's only a couple of minutes then some suppliers give you a better tarrif. Plus it helps them more accurately predict your usage across the year and therefore even out your payments across the year without a nasty surprise of a sudden big bill to catch up

In theory the new smart meters send regular readings directly for you which is even better. My bug bear is that you need a different meter for each supplier so if you shop about each year its dumb. The government did promise they'd all be compatible but screwed that project up somehow.

It all comes out in the wash. Sometimes they over estimate, sometimes under. It rights itself and the difference isn't much.

Readings. No surprises build up then. Or get a smart meter

I forgot to say. If you've got a cannabis farm in the loft, estimate before the harvest.