WAR and oWAR take position into account. So a good hitting 3B or SS/CF will beat a slightly better hitting first baseman.
Most modern stats adjust for position or ballpark. I think Runs Created doesn't do any adjustment but is a counting stat. Offensive Winning Percentage takes RC and calculates into a percentage so longevity doesn't artificially inflate the numbers. Longevity can deflate the numbers since one is less productive as they age, but this seems like the best stat to use.
1. Fielder .702
2. Yelich .691 (will probably go down as he ages)
3. Braun .667
4. Briggs .650
5. Sexson ..641
6. Molitor .637
7. Harper .624
8. Lexcano .614
9. A-Ram .613
10. Scott .608
There are drawbacks to using OWP but there are several stats on the BR site where Fielder is #1 in franchise history. To me it's like asking "who is the best baseball player ever". I'll give you a shortlist and not really care what order they are in. I think the best Brewer hitter ever is Braun/Fielder/Yount/Molitor. They are in the superposition of being #1. Which one you see on top has more to do with how you are looking at them than whether one is better than the other.