#1 Experience

It is difficult to say who has more experience of the two. While Brock Lesnar entered WWE developmental in 2000, and made his main roster debut in 2002, he has taken many leaves of absence from WWE, to pursue his other interests.
Therefore, despite the fact that he's only been with the company for so many years, Lesnar has wrestled less than 200 matches for the company, (and just over 200, if you count his developmental and NJPW run), according to Pro Fight DB.
How Brock Lesnar ruined another wrestler's career - Watch Now!
Reigns, on the other hand, made his developmental debut in 2010 and became a part of the main roster, with The Shield, in 2012. He has already wrestled 879 matches in WWE, well over four times as many as Brock Lesnar.
To pick which man is more experienced depends on your perspective. Does a man who's wrestled for over fifteen years, but primarily as a special attraction, count as a bigger star than one who's wrestled for just over five, but has been in the trenches, every week?
So, there you have it. Here's your preview of the supposed Wrestlemania 34 main event. One where, by all accounts, "The Big Dog will claim the Universal Championship for the very first time.
Let us know your thoughts, in the comments.
A top WWE star is missing in action