Try both versions then you decide, other people will have different opinions, I prefer RS3 but people will disagree with me. After you have tried both and picked which one you like or maybe you will like both there are plenty of starter guides on YouTube which will be much clearer and easier for you to understand compared to someone trying to type it out on a forum post

If you're starting out, go for Oldschool runescape. It's easier to understand and it's more basic. Both are fun but if you've been playing for years, Runescape 3 is impossible to play, it's more like WoW instead of Runescape with all the abilities and graphic updates.

Definitely give both a try but in my opinion, old-school is far better.

Runescape is all about grinding skills for hours to make money which you spend on other skills, doing quests so you can get armor that you can use to make money for other skills, dressing up in silly outfits and standing in front of banks asking people spending money on their skills to give you money, or botting to sell your gold for real money and then getting banned and repeating it. If any of this sounds like your cup of tea, then welcome aboard.

RS3 has combat that requires a bit more of an attention span, but most skills have an AFK counterpart. It's considered the main version of the game.

Oldschool Runescape will seem dull and boring to you if you've never played Runescape, especially during its glory days. However, it's still worth a try.

You could even use legacy mode worlds on RS3 to return to a simple combat system that closely resembles OSRS, but the way that game game is now means that you have to utilize abilities if you want to do high-tier bosses and such. It's kind of a trade-off.

If you decide to play Oldschool, you should consider getting membership, as there aren't very many ways for a low level to make money. If you decide to stay free-to-play, though, you could always get your Woodcutting up and bank the logs you get, then sell them at the Grand Exchange. Don't sell Willows, though, they're useless. Use them for Fletching if you decide to get membership or something. PM me if you make an account for OSRS and I'll hook you up with a starter kit of sorts to get you going.

If you do buy members, though, picking flax in seers village is what everyone does when they first start out. It's always in high demand. Just YouTube "picking flax runescape" if you can't find your way there. Also, look up a guide on the Waterfall Quest. It'll get you some nice combat stats without having to grind for them.

I don't know anything about RS3, so someone else will have to fill you in on money makers and to-do quests.