My vote goes to Lottery Queen. I don't know what she does or how she does it, but her thread is probably the most popular and certainly the most long-running of any I've ever seen on LP.com. Technically, her picks don't qualify as a bona fide "system," but I know she has an undeniable knack and a verifiable track record for picking winners in the Daily Games. I also know that many members have won using the numbers she's taken the time to work out for their states' lotteries.
I'm not aware of any "system" ever being published on the forum, at least not since I've been a member. Every now and then, we'll find a thread where some schmuck is claiming to have discovered some heretofore overlooked nugget, some "inside" information or (my particular favorite) a "Secret" strategy that will allow its users to win on a consistent basis. What usually happens is that the author will get a lot of people jacked up with statements like, "I still have some tweaking to do, but all of my back-testing PROVES that this system WILL work, and I'm just looking for some feedback to find out whether there's any interest out there."
This will go on for quite a while until, finally, the membership becomes fed up with all the teasing, and they'll tell the self-described lottery prophet to put up or shut up. More often than not, a link will eventually appear in a post, sending us to another website such as the one operated by Ken Silver, who pays a commission to anyone who can sell a copy of his "Honest Lotto" system (don't bother looking it up - this is an example, NOT an endorsement). After it becomes obvious that the author is just blowing smoke at people who are too smart to breathe it in, the whole thread simply fades into oblivion and the bottom-feeder who started the whole thing is ostracized and eventually exiled to the outer reaches of cyberspace, never to be heard from again.
To get back on-topic, there are hundreds, if not thousands of lottery systems for sale out there. Some are good, most are trash, but I wouldn't rate ANY of them as "Excellent." Gail Howard offers some very credible and successful techniques at reasonable prices, as does Arlene Meeks, who offers a free downloadable "Player's Guide" to get you started. Some of us like Steve Player's (now OpCom, Inc.) high-end systems but, BE WARNED, Steve Player's Pro Systems require a great deal of study and effort; they do NOT work out-of-the-box. My experience with Steve Player systems has taught me that supplemental charts and graphs are often needed as well, and you'll have to design and make those charts and graphs yourself. Unless you're a pro player and have an extra few thousand dollars lying around that you don't mind investing before you have a significant hit, you should stay away from his high-end systems ($500 or more). I'm sure I'm going to leave someone out so, rather than continue making my own list, I'll let some of the other members ring in with a few of their own favorites.
The tools offered here on LotteryPost.com which, here again, don't qualify as a system per se, are very valuable when selecting your numbers or when you need to eliminate a few digits to bring your chosen wheel down a few notches to make it fit your budget. Learning to use them will save both time and money. Some members even use those tools to help them to identify trends in their chosen games, and they freely and happily share their discoveries with the entire membership so that others can win a few bucks, too.
And there's your answer - there's "The Best Lottery System in the History of LotteryPost.com:" It's the members who make up this community, all of whom are reaching for the same brass ring. When you have 68,000 or so people helping each other to reach a common objective and selflessly sharing information every day, you'll end up with a system which is self-updating, self-improving and self-monitoring, which means it seeks out and rids itself of any flaws or bugs (which we do, whenever necessary, and with a vengeance).
In my opinion, that's a pretty good system, and I think anyone would be hard-pressed to find a better one.