Sarries, Ulster and Toulouse boast strong home records while Champions Cup debutants Oyonnax will make life uncomfortable for teams at the Stade Charles-Mathon, provided they don't lose interest in the competition. Losing bonus points on the road could prove crucial.
Teams: Saracens, Ulster, Toulouse, Oyonnax
Saracens
Champions Cup record: P64 W40 D0 L24
Best finish: Runners-up (2014)
What's hot: Sarries' powerful pack will provide front foot ball and the artificial pitch at Allianz Park works in their favour. Owen Farrell will also keep the scoreboard ticking over from the tee.
What's not: The north Londoners scored just 12 tries in eight Champions Cup games last season and failed to cross the whitewash in the knockout stages.
What's changed: Not much. Saracens have a stable squad and sit top of the Premiership after winning their opening four games.
Key player: Billy Vunipola
Ulster
Champions Cup record: P123 W60 D3 L60
Best finish: Winners (1999)
What's hot: Ulster are in free-scoring form, crossing for 23 tries in seven PRO12 fixtures and averaging over four per game in Belfast.
What's not: Ulster's squad depth will be tested after three Ireland players returned injured from the World Cup. Tommy Bowe may not play again this season, Iain Henderson is likely to miss the first two rounds of the competition, while there is no timescale for Jared Payne's return after foot surgery.
What's changed: Les Kiss has come on board as director of rugby and will know plenty about the squad from his time with Ireland.
Key player: Stuart McCloskey
Toulouse
Champions Cup record: P144 W101 D4 L39
Best finish: Winners (1996, 2003, 2005, 2010)
What's hot: Toulouse have made an impressive start to the Top 14 season, winning six of their first eight games and scoring 25 tries. They are playing a more expansive game under new coach Ugo Mola.
What's not: Le Rouge et Noir possess plenty of star names but question marks remain over their consistency. They crashed out in the pool stages of last year's tournament after a final round loss to already-eliminated Montpellier.
What's changed: Guy Noves has stepped down after 22 years in charge, with Mola taking over at the Stade Ernest Wallon. So far, so good.
Key player: Louis Picamoles
Oyonnax
Champions Cup record: N/A
Best finish: N/A
What's hot: World Cup winner Piri Weepu, George Robson and Nicky Robinson bring bags of experience and visiting teams could be unsettled by the plastic pitch at the Stade Charles-Mathon, apart from Saracens of course.
What's not: Oyonnax find themselves in the relegation mire in the Top 14 after a host of summer departures and European ambitions could be shelved. They were thumped 38-3 at La Rochelle last weekend, their sixth loss in eight games.
What's changed: The coaches. There were a lot of comings and goings over the summer with coach Christophe Urios and fly-half Benjamin Urdapilleta, who was the second-highest points-scorer in last season's Top 14, both joining Castres. Olivier Azam was then brought in to replace Urios, but was fired mid-season following his side's embarrassing La Rochelle defeat.
Key player: Piri Weepu