Title Tiers, Part 1: Cases for and against the East and West favorites

Dynasties have historically ruled the NBA, but we're in an era of nearly unprecedented parity that's produced six different champions over the last six years. This coming season features another deep and diverse field of contenders. We're laying out reasons to believe in them and reasons to doubt them.

First up, the two teams that stand above the rest in their respective conferences, including the defending champs.

Boston Celtics

Reasons to believe: It shouldn't take much persuasion to convince anyone why the team that just won 64 regular-season games, then strolled to the championship with a 16-3 playoff run, is a serious threat to repeat. The Celtics are bringing back everyone who played even an iota of a part in that historic campaign, with their top 11 minute-getters all returning for the title defense.

They still have the league's pre-eminent wing duo stirring the drink in Jayson Tatum and Jaylen Brown, who are squarely in their primes as they enter their age-27 and -28 seasons. They still have the most airtight backcourt in the game with Jrue Holiday and Derrick White, both All-Defensive selections last year. And they still have a pair of centers in Kristaps Porzingis and Al Horford who can space the floor at one end and protect the rim at the other.

Boston remains the only team in the NBA that can create true five-out spacing with playmaking at every position, and it does so without compromising its elite and scheme-versatile defense. In short, the Celtics' best offensive lineups are also their best defensive lineups. That's a rare characteristic, and a big part of how they wound up finishing in the top two on both sides of the ball en route to the third-best net rating (+11.7) in NBA history.

They crafted the most efficient offense of all time (and fourth best ever relative to league average), led the league in 3-point attempt rate, ranked second in 3-point percentage, and turned the ball over at the league's second-lowest rate. Eight players in the regular rotation posted true shooting percentages of 60% or above, and Porzingis busted switches as the best per-possession post scorer in the league.

At the other end, their interchangeable army of brawny stoppers allowed them to switch and cross-match in whatever way they saw fit, and to double the ball less frequently than any other team. That matchup flexibility also allowed them to keep Porzingis and Horford on the back line and out of ball-screen action, which in turn led to the league's second-stingiest rim defense. Their flawless execution of Joe Mazzulla's inventive tactics short-circuited even the most potent offenses.

Porzingis will be on the shelf for at least the first two months of the regular season as he recovers from leg surgery, but all that matters is that he's healthy come playoff time. He played all of 165 minutes last postseason (eighth most on the team), and it barely slowed Boston down. With the rest of the band returning, why would this year's tour play out any differently?

Reasons to doubt: OK, let's say Porzingis isn't healthy for the playoffs. How confident do you feel in his backups? Al Horford is a marvel of modern science, but eventually the wheels are going to fall off for the 38-year-old. (Right?) What happens if the Celtics are left to rely on the likes of Luke Kornet, Xavier Tillman, and Neemias Queta? Depth on the wing is also a bit of a concern. In general, things get pretty shaky pretty fast once you get beyond Boston's vaunted top six.

Sure, that didn't derail the team in last year's playoffs, but that had something to do with them facing a spate of badly undermanned and overmatched Eastern Conference foes before Porzingis returned in a limited capacity for the Finals. They almost certainly won't have as easy a path this time around.

More broadly, I'm not sure the Celtics entirely put the concerns about their playoff offense to bed last spring. Against Dallas, the lone full-strength opponent they faced, they scored just 109.2 points per 100 possessions (which would've ranked 26th in the regular season) and had several stretches in which they devolved into meandering one- and zero-pass possessions. High-end playmaking is still a missing ingredient here, a major factor in those frustrating lulls. And they're still a little light on rim frequency (26th last season) and free-throw rate (25th), leaving them vulnerable to the whims of jump-shooting variance.

In what figures to be a much more competitive Eastern Conference - and possibly a stiffer Finals test, if they get back there - the margin for error will be slimmer this year. - Joe Wolfond

Oklahoma City Thunder

Reasons to believe: The Thunder look like a juggernaut, with few, if any weak spots to exploit. The youngest 1-seed and youngest playoff series winner in league history returns the same maturing and improving core that won 57 games last year, except with Josh Giddey replaced by Alex Caruso and Isaiah Hartenstein.

In Caruso, a Thunder team that ranked fourth in defensive efficiency last season is adding arguably the game's best perimeter defender – an elite stopper who's also developed into a terrific shooter (40.8% from deep on 4.7 attempts in 2023-24). In Hartenstein, Oklahoma City went a long way toward plugging the team's most glaring need for interior size and rebounding help.

Caruso and Hartenstein will bolster what was already a solid two-way supporting cast around the Thunder's young stars. With guard Shai Gilgeous-Alexander now a perennial MVP candidate and All-NBA First Team-caliber superstar, plus wing Jalen Williams and big man Chet Holmgren on All-Star trajectories, the Thunder feel like an almost perfect team coming together at the perfect time.

Oh, and should any mid-season reinforcements prove necessary, Sam Presti's front office still has more draft capital and trade equity than just about any other team. They may not be the defending conference champions, but the Thunder are the class of the West.

Reasons to doubt: This team might still be just a little too green, with NBA history telling us young teams must take their postseason lumps for years before reaching the championship summit. As promising as the career trajectories of Williams and Holmgren are, are they ready to be the second and third options for a title team?

Beyond that intangible question of experience, finding reasons to doubt Oklahoma City's championship mettle feels like grasping at straws. Then again, it's worth noting the Thunder's aggressive approach to defense - in which they surrender the league's highest rate of 3-point attempts from the corners while trying to force the ball out of opposing stars' hands - does leave them more susceptible to an outlier shooting performance. That was a big part of how a seemingly inferior Mavericks team eliminated OKC in the 2024 Western Conference semifinals. - Joseph Casciaro