Ireland's three contenders, reinforced by an aggregate total of six European conquests between them (plus a Challenge Cup), head the cast along with the Warriors.
Munster open their campaign at Sale on Saturday, Glasgow's PRO12 Finalists against Bath at the new enlarged Scotstoun, Ulster at Leicester and Leinster at home to Wasps on Sunday.
Nobody can have made a more emphatic declaration of intent going into Europe than Ulster, back on course after the decisive home win which ended the Warriors' five-match winning start. It all added up to a perfect start for the province's new head coach, Neil Doak.
As an all-rounder of exceptional quality, he once went close to joining a rare breed of dual internationals. Ulster's new head coach played more than 30 times for Ireland's cricket team before going to the 2003 Rugby World Cup as an auxiliary scrum-half.
Within weeks of returning home in the same uncapped state as he left, Doak had experienced another claim to fame - which now acquires some relevance given his native province's opening assignment in the Champions' Cup.
As Ulster prepare to revisit the Tigers' lair in the East Midlands, the memory of their staggering back-to-back ties against Leicester will at the very least have flitted across Doak's mind.
On a cold Sunday under the bluest of Belfast skies in January 2004, Ulster hit their famously formidable opponents with three unanswered first-half tries.
With Doak and David Humphreys pulling the strings at half back, they duly ran in a fourth to win 33-0. As startling evidence that six days are liable to be a very long time in the rugby business, Ulster turned up at Welford Road the following Saturday hoping to give the Tigers the heave-ho.
Instead they lost 49-7, Martin Johnson running more than 20 metres to complete the rout and put the finishing touch to a 75-point swing. Having lost their first 11 European ties in England, Ulster have won four of the last seven, most recently at Welford Road.
Ruan Pienaar accounted for every single point in a 22-19 win over Leicester last season. They will have to attempt an action replay without their Springbok scrum-half, now back in Belfast but another fortnight or so from reappearing for the first time since damaging his knee during the summer.
Doak will not need anyone to remind him that Ulster had to endure some ten years before they finally won on English soil.
He discovered that for himself against Wasps way back 13 seasons ago, so long ago that the hosts were still playing in the capital at Loftus Road with a pack which included the All Black second row, Ian Jones.
Having gone all the way to the final in 2012 only to run into Leinster at their irresistible best, Ulster will settle for nothing less than another serious tilt at the crown they won for the only time at the end of the 20th century.
The day after the wounded Tigers ended their losing run at home to Harlequins, Doak gave his opposite number, Richard Cockerill, a fair idea of what awaits them at Welford Road on Saturday afternoon.
"It's pretty important you get momentum going into Europe," he said in the afterglow of the 29-9 win over the Warriors. "This was an outstanding performance."
Leinster, winners three times in four years, face Wasps at the RDS in what ought to be a monumental occasion for their longest-serving player. Brian O'Driscoll may have hung up his boots but Gordon D'Arcy keeps rolling along, extending a European career which goes as far back as September 1998 with his debut against Llanelli at Stradey Park.
Sunday's game is scheduled to be his 100th in the competition, a fitting tribute to a centre whose longevity knows no bounds. His record includes a hat-trick of tries against Northampton at Donnybrook 14 years ago.
Ospreys - top of the GUINNESS PRO12 pile with six wins out of six after sending the Blues back to Cardiff empty-handed last weekend - begin their campaign at home in Swansea on Sunday as the only unbeaten team on the starting grid.
They will expect nothing less than the maximum five points from Benetton Treviso, having already taken all five against the Italians in the PRO12 last month.
The seventh of the PRO12 qualifiers, the Scarlets, face the most daunting task of all, against Toulon on the Cote d'Azur.
The double champions have already served notice that they intend making history as the first to reel off a hat-trick of victories, thereby going one better than Leicester (2001-2002) and Leinster (2011, 2012).
Despite their inconsistent start, the Welsh region will not be short of an inspiring reminder that nothing is impossible in France.
Eight years ago they pulled off one of the most remarkable results in European history, a win in Toulouse made all the more improbable by the fact that they gave their celebrated hosts a 21-point start and still beat them 41-34 in going all the way to the semi-finals.
The 75-point Ulster swing:
January 11, 2004:
Ulster 33 (Tries-A Ward 2, T Howe, S Stewart. Conversions- D Humphreys 2. Penalties- D Humphreys 3). Leicester 0.
January 17, 2004:
Leicester 49 (Tries- L Lloyd 2, N Back, J van der Westhuyzen, M Johnson. Conversions- S Vesty 3. Penalties- S Vesty 6.) Ulster 7 (Try- D Topping. Conversion- D Humphreys).
PRO12 record in the finals of Europe's premier trophy:
1995-96: Cardiff Blues 18, Toulouse 21 (after extra time)
1998-99: Ulster 21, Colomiers 6
1999-00: Munster 8, Northampton 9
2000-01: Munster 9, Leicester 15
2005-06; Munster 23, Biarritz 19
2007-08: Munster 16, Toulouse 13
2008-09: Leinster 19, Leicester Tigers 16
2010-11: Leinster 33, Northampton 22
2011-12: Leinster 42, Ulster 14
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