Passion. In my first career, I enjoyed it and did very well but wasn't passionate about it. Then I had a near-death experience (knifed in the throat in a homophobic attack) and it made me look at my life. I realised that I was doing a job I was bored by and was looking at decades more work. I'd always been passionately interested in a different career, but hadn't studied it after school because I couldn't afford the 5years of training. I used savings, bursaries etc to retrain and supported myself working nights in a care home and as a masseur. It was a long, hard 5 years and totally worth it. I'm still in my new career 15 years on and I'm still as passionate about it as I was when I first started.
Go passion, without a doubt.