This has been a subject of discussion for many years, with various scientists supporting either of these two great cats. Naturalists of African origin tended to side the lion, whilst Asians had a bias for tiger..... Since records started being kept, these two apex preditors had seized to exist side by side in the wild, thereby eliminating the chance for scientists to establish which of the two cats where dominant in areas where historically the range of the two species over-lapped.....
What ever the case may be, we do know that amongst different species of predators, the lion and tiger are amongst the most evenly matched, so much more so that they occupy the same positions in the 'food-chains' of their various local environments.... Whatever formidable beast that a wild tiger has been able to single handedly defeat in Asia, a lion has been able to replicate the same on a beast of comparable size and strength in the wilds of Africa...... Even more interestingly, scientists have noted that when you 'skin' a dead tiger, the body is virtually unrecognizable from that of a 'skinned' lion, unless a DNA test is undertaken on the (skinned) carcass.....
In captivity, lions and tigers have often been kept in the same enclosures, where neither species have ever taken consistent 'control'.... There are male lions that have been totally dominant of enclosures containing even the biggest Siberian tigers, and conversly, tigers have also dominated where lions are involved..... Fights have also broken out, and often the lion has been the victor, at other times, tigers have won..... Notably, approximately two weeks ago in a Korean zoo, an adult male lion killed an adult female Siberian tiger that was only lighter than him by 20 kg......
A lot of analysts place emphasis on weight, though in reality the weight difference is negligable. The tiger is only slightly larger consistently...... For instance, an average male 'Bengal tiger' weighs in at approximately 500lbs with exceptionally big males reaching 600lbs or so (especially in Northern India, and Nepal). An average male lion weighs in at around 450lbs, with big males reaching about 550lbs..... A wild Kenyan lion weighing over 600lbs was once shot, and the lions of North Africa (now extinct in the wild) averaged in at 500lbs, sometimes crossing the 600lbs mark. Recent studies have also shown that very large 'Bengal tigers' often out-weigh average seized 'Siberian tigers', which typically weigh in at around 600lbs or so. Interestingly, the lion in turn is larger than many of the southern tiger races of Asia, some of which have become extinct within the past 100 years or so (Surmatran, Javan, Bali, etc). Indeed, many individual lions are bigger than many individual tigers of the same sex and age....
However, of greatest interest is the outcome of wild populations living side by side.... We know that lions had lived side by side with tigers through-out much of Asia up to 150-200 years ago.....but records where not kept of the interaction between the two species.... In India (which is home to the last remaining population of wild Asian lions), plans are afoot to create a new lion population in Kunor Palpur, a protected wild area in Northern India were lions were formerlly present, and which is also home to a population of wild tigers....
In summary, I would have to favor the lion, not because it is a more formidable cat individually, but primarilly because of behavioral traits of the two species. Wild tigers are solitary cats, coming together rarely. Quite unlike lions, which have a tendency to congregate in groups. So, whilst it is possible that a single tiger may be able to harrass or even kill a single male lion, as tiger or lion often do to leopards, it is most certainly impossible that any tiger would survive an onslaught from a coalition of pride or nomadic males or even a group of females defending their young. Lions are well known for 'ganging up' against all kinds of adversaries, even 'prey', and animals that a single lion can easily defeat. Most certainly, it is over-whelmingly obvious that any existence of the two species side-by-side will create the kind of of rivalry that has yet to be documented in the animal kingdom. One cannot think of two other separate species that are more evenly matched pound for pound, as well as in terms of courage, and ferousity than the lion and tiger. Additionally, it is almost un-imaginable thinking of either lion or tiger as the second top predator in any environment... Tiger or lion populations are thought to be fearless of predators in any environment in which they exist, and are always top of the 'equation'.
Finally, it is most noteworthy that ancient literature and cultures, from areas where the two species existed side-by-side, have a tendency to depict the lion in a manner that is symbolic, more so than the tiger..... Even in the bible, the lion is consistently referenced as an animal of strength and courage, as against that of the tiger, in areas such as Babylon (Iraq), and Persia (Iran), which was also home to the now extinct 'Caspian Tiger'.... Wether that symbolizes dominance by the lion, we do not know, but it most certainly goes in favor of the lion in regards to which of these two apex predators is the more dominant....