Should I join a start up where job security and pay is less or a well established company where there's more pay with less learning curve ?
Please help me decide.

Start up early on. Enterprise later closer to retirement

That's a decision only you can make.

You know the work environment you like. You know the companies. You know you. We don't.

Depends on your age and what you're looking for right now in life.

To consider the startup- I’d encourage you to ask them questions about their financing. In my opinion, you want to avoid the ones where your direct manager is overly financially involved (I.e Mortgaged their house / cashed out their retirement fund) . Those are the ones that will compromise ethics, and burn you with unrealistic deadlines for the sake of cash.

Also, depending on the size of the startup and your own family — expect longer work days , mandated weekend work, etc. if you don’t have a family and kids, it might be just fine — and the payout could be big... but I missed out on a lot of my kids sports practices while working weekends.

Wait! Less pay!?!? Startups often pay more because they know it’s harder work.

Depends, if I was in that situation I would have to really believe in what the start-up was doing.

Big company does not mean lower learning curve. Big companies are more likely to deal with niiiice, big and heavy projects where you will learn a f****** hell of things. Also do not underestimate the learnings from inter cultural challenges.