So you already expored the vast content you can find on usenet by signing up to an nzb indexer like nzbwolf.com - The next thing you need besides a download program like sabnzbd is an usenet provider.
Some people believe the usenet landscape is dominated by one company called Omnicron Media, that has the evil plan to take out all the competition. The believ is, they have lots of shell companies and own some of the most popular usenet resellers. Originally Omnicron is a wholeseller, so yes they are really big and important, the rest are just rumours.
To the regular enduser (not the pro usenet expert) this is currently not important, in the contrary, the price battle between different usenet providers means saving a lot of money for the regular guy. Thank god, we do not soley depend on Giganews and their 15$ per month pricings for a basic account anymore. So ignore all the wining by some users and even mods on reddit about Omnicron and enjoy the low prices while you can. Building up a real monopoly on usenet access is impossible and will never happen, because there is no network effect. Nobody cares if your usenet provider has 100 or 100.000 users. Nowadays not even the retention is a real selling point anymore. Retention in the usenet world is the period of time the usenet provider is storing old binary posts so you can still download them. For example a binary retention of 1000 days means, you can theoretically still download a movie that was posted 2 years ago. But today it is just theoretically, because the regular content you want is taken down my DMCA-request in a matter of days. Some nzb indexers provide obfuscated uploads that might withhold the DMCA-regime a little longer but sooner or later it will be taken down. Today even adult content is taken down by DMCA, but much less than movies and tv shows.
So lets get to the point of what is important when choosing a usenet provider.
Anonymous and No-Logging-Policy
You should not connect your personal details like credit cards or home address information or your paypal account (avoid paypal anyway) with your usenet provider. Doing so it not really a risk, but even if there is a small chance that one day you might get problems because of it (usenet provider gets hacked for example), you should avoid it because it's not hard at all.
Many usenet providers offer payment methods where you share only your email address with the provider. Bitcoin should be your preferred payment method. Most of these providers offering bitcoin as payment also promise not to log your downloads. Even though you cannot verify this promise, a promise is still better than an agreement that they log everthing they want.
If you spend money on a yearly usenet plan (to get more discount), you trust the company to be around for another year at least. You also trust the company to offer the same quality of service throughout the year. Either you already used the usenet provider before or you stick to a monthly plan in the beginning and switch to a yearly plan later on. The longer your usenet provider of choice has been around and the better his reputation is in the community the less chance there is that quality of service is suddenly interrupted.
Do not always choose the cheapest, or you might pay twice. There are reasonably prices for usenet access, depending on the maximum speed you will get. If your timing is good, you might even get an extra discount for your favorite provider. Don't overpay for usenet - be willing to pay a reasonable price and watch out for usenet discounts.
Depending on your own internet connection speed choose a provider or a package that is able to max out your internet connection. If you have slow internet connectivity anyway, you might be able to save some costs on your usenet access, since you can choose a cheaper usenet package.
Some general advice
Beware of some shady companies that try to lock you into long term contracts with initially free testing accounts. A good usenet provider does not force you into auto-renewal and offers monthly and yearly contracts. The choice should be yours.
It is not always the best option to choose a provider on your home turf. Usenet is not about ping and roundtrip timings, so it does not really matter if you connect to a datacenter on another continent or in your home country.
Always remember that most providers in Europe have to pay 19 to 25 percent value-added tax. Sometimes it might be helpful not to disclose your real home country and try a fake one. Customers from the US normally do not have to pay the value-added tax towards european countries.