ESPN's rugby predictions: Players to watch, key head-to-head & more

All eyes are on Bilbao this weekend as Leinster, Racing 92, the Cardiff Blues and Gloucester contest this season's European finals.

So, as fans from England, France, Ireland and Wales nervously check into their hastily booked -- and pricey -- Basque accommodation, we look at where the games will be won and lost.

Player to watch

Champions Cup: Leone Nakarawa (Racing 92). The impossible-to-miss Fijian was not at his gasp-inducing, impossible-offloading best against Munster in last month's semifinal, but he will have you on the edge of your seat from the moment you realise he's about to get the ball on Saturday. He's huge in the lineout, 6-foot-5 of ball-snagging knotweed at the breakdown, has the footwork of a back courtesy of his Sevens experience, and a self-sustaining engine that can take him the entire 80 minutes. Whether he plays at lock or in the back row, he will be a giant-sized handful.

Challenge Cup: Nick Williams (Blues). Forget flash harries like Welsh Rugby Writers' Player of the Year Josh Navidi, or Young Player of the Year Jarrod Evans. Look to the old men of the club, such as permanently battered, never beaten No. 8 Williams. He will take that ball and crash into opposition ranks, breaking the gainline time and time again. Or he will stand like a man mountain in defence, letting attackers know via the medium of bone-jarring tackles that they will not pass. Williams, now 34, is the beating heart, the driving legs and the never-say-die will of the Blues. Treasure moments like this final with him.

Key head-to-head

Champions Cup: Leinster vs. Racing, Saturday, 4.45 p.m. (BST)

Johnny Sexton vs. Dan Carter. It's likely to be your last chance to see two of the greatest 10s of their generation -- arguably of any generation -- go head to head on the biggest stage in European club rugby. Even if it's just for part of the game, it's the stuff of rugby dreams. Age may have wearied Carter, 36, but the years have not entirely condemned him just yet -- despite what you may have read elsewhere. And he wants a European Cup winners' medal before he heads off to the sunset in Japan. In his way stands Leinster and Ireland talisman Sexton, 32, a player not in the business of giving any quarter. Say no more.

Challenge Cup: Cardiff vs. Gloucester, Friday, 8 p.m. (BST)

The back-row battle -- Navidi, Jenkins and Williams vs. Polledri, Ludlow and Ackermann Jr. -- looks especially tasty. Breakdown kings Navidi and Polledri have racked up 18 turnovers between them in the Challenge Cup this season, with the Blues' dreadlocked flanker so far shading the stat challenge 10-8. Italian rising star Polledri, meanwhile, has justifiably garnered a fair few plaudits of his own, with bullocking charges and a ridiculously near-perfect high tackle rate to add to his nuisance-making abilities at the ruck.

Deciding factor

Champions Cup: The scrum. Word is Racing could start with a monstrous pack that weighs in at close to a metric tonne -- give or take a kilogram -- which wouldn't so much hint at a penalty-reliant game plan as shake the Earth to its very core with the idea. Such a tactic has its pros and cons. A scrum that size is almost certain to do some serious set-piece damage. But a big pack will also run out of steam, leaving the Top 14 side vulnerable in the final quarter if they haven't built up a big enough lead. And Leinster will take advantage of any weakness from first whistle to last.

Challenge Cup: Playing style. Johan Ackermann's Gloucester have an expansive rugby habit which can be thrilling to watch -- and they have a tremendous try-scoring record in the Challenge Cup this year. But if they get it wrong and play just a little too fast and loose, as they have too often since the turn of the year, then they could fall to a sucker-punch from an organised Blues side high on confidence after winning eight of their last nine in the PRO14.

Prediction

Champions Cup: Leinster rightly start as favourites to claim their fourth, Toulouse-equalling, title -- and first since 2012. But, with wise triple European title-winning heads Leo Cullen, Cian Healy, Johnny Sexton, Isa Nacewa and Devin Toner in the dressing room they will not fall into the trap of believing the media hype surrounding them coming into the final. Nor will they underestimate their opponents, who have rediscovered the art of competing on two fronts. Two seasons ago, Racing's Champions Cup final defeat to Saracens prompted a rapid response in the showpiece Top 14 match against Toulon. They're made of even sterner stuff these days. Even so, it probably won't be quite enough. Leinster by 7

Challenge Cup: The two sides' overall domestic records this season are strikingly similar, for all that the Blues' recent form is better than the Cherry and Whites -- with both recording 11 victories and 10 defeats in their respective leagues. Gloucester have by far the better try-scoring record in the Challenge Cup, but breaching that Blues defence will take something a bit special. This is going to be closer than many people think but, in the end, the Premiership side could just shade it. Gloucester by 5