Saddle bag or rucksack - what's best?

For the commute - what’s more efficient - carrying tools in a rucksack (which already has a change of clothes in it) or using a saddle bag?

Does it make any difference adding weight on the bike or to rider?

And by tools I mean; spare tube, multi-tool, tyre levers, mini-pump - so nothing massively heavy.

It depends.
If you use the bike for anything else that is not commute, then the saddle bag is a better choice, because you will not forget stuff on the rucksack.

the saddle bag is a better choice

Saddlebag, no brainer.

Always having spares/tools on the bike wins over having them in something else in almost every situation. I can’t tell you how many times I’ve forgotten something when commuting by bike just because something got out of whack from the normal routine. I’d hate for that forgotten thing to be a spare because I used one last week and forgot to replace it!

Is your bike being left somewhere where the saddle bag could be stolen, if so, put it all in the rucksack.