As Bitcoin (BTC 1.54%) keeps bumping frustratingly into the $30,000 mark and down again, some cryptocurrency fans might lose patience and bail. That's a shame, as the HODL (Hold On for Dear Life) strategy has richly rewarded many of Bitcoin's long-term investors.

Meanwhile, some investors would prefer to stay in the world of stocks and exchange-traded funds (ETFs) rather than dabble in direct cryptocurrency trading. For example, some types of retirement accounts might not permit Bitcoin buying and selling. Until a full-fledged spot Bitcoin ETF is approved, you may prefer an indirect play (or two) on Bitcoin's potential upside through shares of crypto producers.

While Riot Platforms (RIOT 5.35%) and Marathon Digital Holdings (MARA 0.66%) don't have one-to-one correlations with the price moves of Bitcoin, there's definitely some overlap. So, if you're ready to wager a moderate sum -- say, $1,000 in total -- on a couple of premier Bitcoin miners, let's take a closer look at what makes Riot and Marathon stand out in 2023.

Stick to the big producers

First and foremost, you won't have to worry about liquidity issues with these two crypto picks. Riot Platforms and Marathon Digital Holdings have approximate average daily trading volumes of 22 million and 38 million, respectively. Furthermore, these two stocks are well above $1, so they're not in imminent jeopardy of being delisted from the Nasdaq exchange for violating minimum closing-price rules.

In other words, your $1,000 total bet on cryptocurrency miners should feel safer if you stick to the bigger, more established producers. Both of these companies have market caps in excess of $2 billion, so Riot Platforms and Marathon Digital Holdings check that box, as well.

Granted, bigger doesn't always mean better and there's always volatility risk in the world of cryptocurrency. Therefore, it's wise to invest no more than $1,000 in total on these two companies, and to divide this into $500 per stock so you won't lose everything if Riot or Marathon goes down the tubes.

Focus on nontraditional metrics

If you're going to invest in these two names, I don't recommend obsessing over traditional valuation metrics. It's not unusual for crypto-related businesses to have multiyear road maps to profitability and therefore currently be unprofitable. Riot Platforms and Marathon Digital Holdings fall into the pre-profit category, so don't bother trying to look up their P/E ratios -- they have no earnings to speak of.

I'm not suggesting that the value of these businesses to their shareholders doesn't matter. Rather, I'm only saying that value in this category might have to be assessed differently. For example, you might choose to consider Riot's and Marathon's revenue growth as an appropriate litmus test.

As it turns out, Riot Platforms grew its revenue from $46.2 million in last year's second quarter to $49.7 million in Q2 2023 -- not a massive change, but fairly decent given Bitcoin's price stagnation. Marathon Digital Holdings, meanwhile, saw a jump from $24.9 million in revenue during the year-earlier quarter to $81.8 million in the second quarter of 2023.

Along with top-line growth, prospective investors can examine the recent Bitcoin mining activity of these two companies. Riot Platforms produced 1,775 Bitcoins during this year's second quarter, versus 1,395 Bitcoins in the year-earlier quarter; Marathon Digital Holdings demonstrated an even greater ramp-up as it produced 2,926 Bitcoins in Q2 2023, compared to only 707 Bitcoins in the same quarter of 2022.

Again, there are no guarantees of fast gains and volatility will be an issue for some investors, as both of these stocks tend to follow and/or amplify the moves of Bitcoin. Thus, risk mitigation is crucial. This can be achieved by limiting your position sizes to $500 in Riot Platforms stock and another $500 in Marathon Digital Holdings stock -- bold bets, indeed, for HODLers on two prime producers of the world's best-known cryptocurrency.