I don’t know which asset to purchase

I am 43 and have not had a job that afforded me to start a retirement plan or that had a 401(k). I went back to college in my early 30s and did grad school. I am in my first job and most likely my last as I have an opportunity to buyout the owners of the company in 5-10 years. I have a simple IRA through this company with American Century Investments. I am currently only contributing 2% to get the company match of 2% while I pay off credit cards and other debts accumulated through my schooling. I did not want to miss out on the free money though. Once those debts are paid off, I plan on contributing more.

Which would be my best asset? Should I go with the high risk/high reward or low risk/low reward? What can I look at in the assets to understand which category it falls into?

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Atm I am just in the default asset.