To answer your question quite simply. Mike Sigel had the better record in 9-Ball. As a matter of fact, I don't know of one that has a winning record against Mike in the 80s and early 90s.
Mike is the most winnegest player in pocket billiards, and still is. Also adding in the fact Mike retired much to early (while still playing excellent pool), he no doubt would have certainly went on to win much more if having continued. I don't think the financial rewards of pool kept his attention in playing pro events (that's my opinion).
Someone above said Earl was an awesome ball pocketer, and this is true. However, Mike was certainly as good or better at ball pocketing. I personally have never seen anyone who could come up with the really really difficult shots in the most high pressure situations so consistently as Mike Sigel. He thrived on the times many of us would be shaking from the sheer pressure. Another talent Mike has that is really hard to come by is the ability to quit the pro level for years on end, come back to the game, and run a 150 n out on ya.
9-Ball would be the closest game between Mike and Earl. All other games would certainly favor heavily on an 80s Sigel. To show how dominant Mike was we have facts. Having retired much to early, other players have went on to play another 20 years, and still not reached the amount of majors Sigel has won.