When it comes to the best lines in the NHL, Ryan O'Reilly has an expert opinion.

He has centered a few great ones during his career, but the St. Louis Blues star is more familiar with having to defend against them. Like that one on the Dallas Stars that's currently reigning over the rest of the NHL: Jason Robertson's line with Joe Pavelski and Roope Hintz.

"I just remember playing against them, you had to work to close that gap and be tight to them. Because if you weren't close, they're dynamic. They're gonna be making plays if there's that separation. They'll just eat you up," O'Reilly told me recently. "One little breakdown. One little bit of separation. The next thing you know, it's in the back of the net. So it's extremely tough against those guys."

That's what the great lines do. O'Reilly said the key to the best ones is the way they read the play, which is what Robertson's line does so adeptly. Three talented players, acting as one. Even a single line like that can be an energy source, powering a team for weeks.

Here's our ranking of the top 20 lines in the NHL this season. Keep in mind that coaches, by their nature, frequently chop up their lineups. Hence, some of the groups here might no longer be together at the moment but could be down the line. Also, that line mixing meant some players were left out of the ranking: Kevin Fiala has had a good season for the Los Angeles Kings, but he has spent at least 10 minutes with six different line combinations.

Injuries played a role, too. The Colorado Avalanche had two line combos that were outstanding last season. But injuries to Gabriel Landeskog, Valeri Nichushkin and now Nathan MacKinnon meant they didn't make this list.

The basic standards for this ranking: We looked at lines that played a minimum of 75 minutes together at even strength. We tried to balance actual results with underlying numbers. In some cases, we've rewarded lines for the work they've done. In others, we're ranking them based on how they project with additional ice time together.

Here are the top 20 lines in the NHL so far this season. Stats courtesy of Money Puck, Natural Stat Trick and Evolving Hockey.