Early levels always use cannon. You can get like 1-50 range in an hour.
Past 70 I'd say just train all combat with slayer and you'll be 99 if not close to it with all combat styles when you get 99 slayer.

Just that reaching 99slayer takes ages

Not really. Every time you want to train combat, just go to slayer and you will train combat, slayer, and make money rather then just training combat.

can do slayer before 70? im 43/55/40/45 right now

Yeah you def can.
It's going to be a bit slower training it though.