Given the questions you've asked and knowledge you currently posses, you're already on the right track OP.

I'd open up a Vanguard account and go through their list of ETFs:
https://investor.vanguard.com/etf/li...th-end-returns

If you want something more "stable" the Mega Cap Growth ETF (MGK) and Growth ETF (VUG) funds more or less follow the S&P 500.

If you want something more focused, the Information Technology ETF (VGT) and Consumer Discretionary ETF (VCR) funds typically outperform the market and have shown strong YTD gains thus far.

Not sure why peeps keep referring you towards an "expert" though; any/all data you need on the stocks mentioned is all at your finger tips. All an "expert" will do is steer you towards something like American Funds which are actively managed funds with crazy high expense ratios.

My only other suggestion is to pick one and leave it. The more you obsess over looking at gains/losses every day and/or try and shuffle funds from one to the other all the time, you're not gaining anything.