The past year has been a roller coaster on Wall Street, and under such conditions, it can feel particularly daunting to invest new money into the stock market.

While nobody knows for certain when the current bear market will give way to a bull market, we can be fairly sure one is coming eventually. And that makes this an opportune time to invest with the goal of taking good advantage of that eventual upswing.

But whenever one buys, it's important to choose the right investments. Exchange-traded funds (ETFs) can be fantastic options for many people, and there are two ETFs, in particular, that I'm putting more money into right now.

1. Vanguard S&P 500 ETF 

The Vanguard S&P 500 ETF (VOO -0.07%) tracks the S&P 500 index, which means it includes the same stocks as the index and is designed to replicate its performance. This ETF contains stocks from 500 of the largest public companies in the U.S., including big names like Amazon, Apple, and Microsoft.

An S&P 500 ETF is a relatively safe investment that can still earn you substantial returns over time. Historically, the index has had an average return of around 10% per year. In other words, between the up years and the down years, its overall gains (including dividends) have averaged out to around 10% annually over the long term.

While that may not sound like much, growth like that can add up. For example, if you invested just $200 per month in a fund that earned a 10% average annual return, after 25 years, your investment would be worth around $236,000.

However, despite being a powerhouse investment, the Vanguard S&P 500 ETF is also one of the safest ETFs out there. The S&P 500 has experienced dozens of corrections, crashes, bear markets, and recessions over the years, and so far, it's recovered from all of them and gone on to hit new highs. So while there are no guarantees in investing, it's extremely likely this ETF will rebound from the current bear market, too.

The Vanguard S&P 500 ETF is a particularly strong choice because of its low fees. It has an expense ratio of just 0.03%, which is among the lowest of all ETFs. Investment fees can cost you tens of thousands of dollars over time, and this particular ETF not only delivers strong returns, it also lets you keep more of them.

2. Vanguard Growth ETF

The Vanguard Growth ETF (VUG -0.02%) contains 253 stocks from companies with the potential for rapid growth.

Growth ETFs are designed with the goal of delivering above-average returns, so you're more likely to see higher earnings with this type of investment than you would with an S&P 500 ETF. While an S&P 500 ETF aims to match the market, a growth ETF attempts to beat the market.

Over the past 10 years, the Vanguard Growth ETF has earned an average rate of return of close to 13% per year. If you invested $200 a month in a fund that earned a 13% average annual return, you'd accumulate more than $373,000 over 25 years.

The downside to growth ETFs, however, is that they're riskier. Shares of high-growth companies, in general, tend to be more volatile than those of their more established counterparts.

With this type of investment, it's especially important to keep a long-term outlook, and be sure that you have the stomach to ride out the roller coaster of volatility. Finally, double-check that your portfolio is well-diversified.

Nobody knows how the market will perform over the coming weeks or months, but eventually, this downturn will give way to a bull market. By investing now, you'll be well-positioned to take advantage of it.