Is there a good basis for reaching an objective conclusion?
There are plenty of facts out there to help, I suppose. And there are lots of bases to examine the question from. But no one can reach a definitive answer, since there is no definitive answer to the job of a general.
Here are a few angles you could look at it from:
Did the general consistently outperform the other generals in his own army on the battlefield and on campaign?
Did the general consistently win his battles when the numerical odds were even or in his favour?
How many times, and in what proportion, did the general win against the odds?
Did the general consistently bring a higher proportion of his troops into action than his enemies did in a given campaign?
How many really crushing victories in battle and on campaign did the general achieve? How many did he receive?
Those might help focus on the issue, but there can be no right answer to how the different facets should be weighted.
IMHO, it is more straightforward to make a case for Wellington than Napoleon (note that does not necessarily mean I think he was the better general), because Wellington scores highly on every criteria I can think of. Napoleon would score very highly in many areas, but isn’t as consistent: he has many more defeats in battles and campaigns to compensate for.