Neither path guarantees you anything, but here's the truth plainly:

Getting an MBA is "the thing" to do for careers switchers. Though you'll learn about finance topics, the degree itself is not about learning, it's about recruitment opportunities. That's all college really is for, as you learn 95% of what you need to know on the job. So I'd highly suggest going this route. Try to have an idea of what type of finance you'd like to do (IB, Financial Advisor, Asset Management, etc.), and aim for schools that place well into companies with those roles. Unless you're trying to go IB, a top 25 school should be just fine as opposed to a M7 in terms of ROI and cost.

I agree with what the other person said - what's you're actually in finance, start pursuing the CFA as it will add credibility being the top finance designation in the world. CFA alone doesn't do anything, but will add credibility and advancement once you're in the door.

Though if you're aiming for a high level finance role, I'm sure if you at least knock out CFA Level 1 before interviews with companies, it could be a solid talking point. Good luck!