With more than 2,000 U.S.-listed ETFs available to investors, it's easy to get confused and overwhelmed with the sheer number of choices. And with so many options, how do you know what's good and what isn't? In this space, I'm going to evaluate and rate a popular ETF to help you make smarter investing decisions.If you want to receive these reports when they're published, click that "Follow" button on my profile. Do you have an ETF you want profiled? Comment down below!Today's ETF is the Amplify Transformational Data Sharing ETF (BLOK).You may not recognize which sector this ETF targets by its official name, but you've no doubt heard its more commonly used name - blockchain. This was one of the very first blockchain ETFs to launch and, thus far, has become the most successful with just over $135 million in assets.ETF Website: Amplify Transformational Data Sharing ETFBLOK is an actively managed ETF that invests in companies actively involved in the development and utilization of blockchain technologies, the tech that underlies bitcoin and other cryptocurrencies. How does it define "actively involved"? The company must either be actively engaged in research and development, profiting from the demand for blockchain applications, partnering with or investing in companies engaged in blockchain development and acting as a member of consortiums or groups dedicated to the exploration of blockchain technology. Companies considered to have greater exposure to blockchain are given higher weights in the portfolio. If you've been a follower of my work on ETFs, you'll know that I'm not a fan of blockchain ETFs. That's not necessarily because of anything inherently flawed in the ETFs (although some of them have a few issues), but more because there's so little pure blockchain exposure. Goldman Sachs (GS), which is one of BLOK's top 10 holdings, is making big investments into blockchain but if you buy Goldman stock, you're obviously getting exposure almost entirely to their banking business, not their blockchain investments.That being said, I think BLOK is probably the best blockchain ETF of the bunch. It's actively managed, which is important in such a rapidly changing and developing industry like blockchain (the next three largest blockchain ETFs are all index-based which prevent them from responding quickly to industry developments). It's also priced roughly on par with its passively-managed counterparts. Active management usually comes with a higher cost, but in the case of BLOK, you're getting an active fund with almost no price premium. These two factors, I feel, are BLOK's biggest selling points.But blockchain is very early in its development. Trying to pinpoint pure blockchain exposure within a portfolio will be incredibly difficult. Almost all of the companies developing blockchain tech have core businesses in other disciplines, so you'll frequently be investing in a financial or tech company instead of a blockchain company. There may never truly be a "good" blockchain ETF.Recommendation: Stay AwayIf you're bound and determined to own a blockchain ETF in your portfolio, this is probably the one to buy. But I wouldn't be buying blockchain ETFs at all right now for the reasons mentioned earlier. With an expense ratio of 0.70%, you're probably better off just buying a broad ultra-cheap tech ETF, such as the Technology Select Sector SPDR ETF (XLK), and save yourself a lot of money on fees.What do you think of BLOK? Comment down below!