Avoid leagues where there aren't strong rules and harsh punishments for tanking. If you are starting one, you will likely end up with a couple of owners who you will later regret having, but after a few seasons, your will have a core that jells together.
There is genuine tanking, and there is subtle tanking. Most progressive leagues have rules to curb tanking, such as minimum IPs and ABs, and win floors (ie. 36 wins required by game 120 to be eligible for the first pick in the draft), and ejecting owners who clearly are tanking (such as putting your ace pitcher, who is at 100% strength, in AAA; trading away all your starting pitching to get draft picks, leaving your starting rotation full of relievers; or trading away great long-term players for someone who has a superb year coming up - suggesting the owner won't stay around after he wins that season). But everyone who is approaching game 120 usually figures out where they expect to be in the draft. If two teams have 36 wins with one game remaining, each one may decide to rest stars to increase the likelihood of a loss to get that #1. Small moves like that usually aren't considered tanking, but clearly are designed to lose to get a better draft pick. If your choice in the draft is, say, Bert Blyleven (career WAR of 96.5) as the #1 pick and a pitcher with half that career WAR as the next best player, it makes sense for you to do all you can to get that #1 pick. Those moves are allowed unless they are particularly egregious.
It all comes down to trust. Progressive leagues work well when they have been around for a long time and they only need a new owner on occasion, because each new owner is a risk. When someone asks to get into a progressive league, there usually is some research done to figure out whether he/she has tanked in other leagues.
I would strongly urge you to play in a progressive league before trying to commission a new league. It's pretty miserable being a commissioner in a league that has multiple problem children, and you will certainly have problems if you don't have a firm set of rules. You will also have a hard time recruiting for that first season if the other potential owners know you have no experience in commissioning. Good luck!