I think you should always train with OSRS gold slayer, it should not take too long to get 70 in all; maybe a few days depending on the length of time you play each day. A great set-up for slayer which is fairly cheap is to use - Slayer Helm or even Neitznot (sp?)

Bear in mind that's only a proposal for gear, you can always change things up. For example, you may swap out your guardian to get an Obsidian shield should you feel like you need the extra defensive boost, and you could always use dragon plateleg's if you do not want to be fixing your barrow's armor because it excels in battle.

Furthermore, if you do not have the quest requirements for your helms, DO THEM. If you plan to do any slaying whatsoever you ought to do the Smoking Kills quest after possible. Do not be afraid to try out different things and see what works for you.

This entire setup will cost you approximately 2-2.5M, and is an excellent overall setup for slaying. Remember to also use a number of that money to buy super sets (Super Strength/Attack/Defence potions) that you ought to be using on ALL your slayer tasks. It may look like you are spending a lot in the beginning but it speeds up your tasks clearly and cheap RuneScape Mobile gold is well worthwhile, and you will be profiting from your slayer drops / hint scrolls anyway.