Take finance but remember 95% of the investing stuff they teach you is worthless because its all based on the efficient market hypothesis. You must pretend to believe this and understand it if you want to get a job in finance though. Trend lines, support and resistance are definitely not something you should waste too much time learning. Take a look at Austrian Economics, read Economics in One Lesson by Hazlitt.
Major in behavioral psychology and writing, and pick up minors in statistical math and accounting. With these you'll be set for any kind of business venture you may chose to pursue.
Maths, computer sciences and history....and try to keep an independent mind. If you find some time for physics, it might be useful too...
Do both, I did. Economics gives you good theory and math skills and Finance will give you more specifics about the markets.
Do a business degree, then you will study both; I would recommend majoring in finance though. I had to do three mandatory econs for my business degree (intro microeconomics, intro macroeconomics, intermediate microeconomics), which give you a pretty good start on what economics is all about. I've completed all of my finance classes now for the degree, and I'll be doing a few econ classes next year to finish up my remaining credits. Finance will provide you with a great deal of the background info that you need in order to approach the markets, just remember to think critically about what you are learning. There is also quite a bit of overlap between some undergrad level finance classes and economics.
Then what classes should we take to improve our trading if economics and finance classes won't do it?