The Rackets with the best payouts for the Cash and Job Rackets are on the shortest timer (4 hrs). Given that Rackets don't "bust" until 8 hours after a Racket has finished, this provides a maximum of 12 hours between the point at which you invest and the time at which you need to collect without losing your Influence investment.
Losing your Influence Investment[]
Influence regenerates at a rate of 1 point per hour. If you allow a 16 point Racket to "bust" then you lose 16 hours worth of progress building up Influence.
It is therefore critical that you manage your Rackets in such a way that you don't allow yourself to lose Influence to busted Rackets. A loss of six 16 point Rackets is the equivalent of losing 4 entire days of Influence gain.
Influence Management[]
Depending on your real life schedule, you may or may not be able to check back as often as every 12 hours. So what if you need a longer break?
The “Hold It” Strategy[]
The basic theory of this strategy is to collect your Influence and if you know you are going to need to take a break to "Hold" it until you next log back on.
For example, a player with Taxi Stands in every slot (all 20) would have about 100 Influence invested. It would take roughly 85 skill points invested into Influence in order to “hold” all 100 Influence points. This has the advantage of allowing you to take a break for an indeterminate amount of time and still be able to reinvest into all 20 slots with Taxi Cabs the next time you log back into Mafia Wars.
The obvious advantage to this strategy is that you can easily take very long breaks away from the game and still have a large pool of Influence ready for investment when you get back. The less obvious advantage is that the larger Influence pool will freely allow you to invest in almost any Racket.
However, this strategy is not advised due as your skill points can likely be better used for other stats. Influence in this respect, is similar to Health in that it is not efficient to have excessive amounts.
The Racket Rotation Strategy[]
The idea here being that you invest in much longer Rackets to avoid losing all your influence to busted Rackets. The ideal would be to have some rotation setup so that you could immediately reinvest back into the 4 hour jobs the next time you logged back into Mafia Wars.
With this strategy, the Racket payout is irrelevant. You need to look at length of time and Influence cost. You want a Racket that is long enough for you to take your break and has an Influence cost that complements the Racket you normally use.
For example, the "Strip Club" Racket lasts 22 hours and costs 10 Influence. The "Taxi Stand" Racket lasts 4 hours but costs 5 Influence. If you know you won't be back in 12 hours (4 to complete + 8 to bust) to collect your next "Taxi Stand", then you can invest 2x "Taxi Stand" into one "Strip Club" and return in 22 to 30 hours.
The "Strip Club" payout of $11,300 is only secondary. The real purpose is to avoid losing the 10 Influence.
One caution. It is possible to overflow your influence capacity and lose influence if you collect too many large rackets at once such as by using the collect all button.
The Energy Boost Strategy[]
As long as you are capable of collecting every 4 hours, having all of your influence invested in the the Jobs tier can result in an energy boost of up to 45 to 90 points/hour. Once you have purchased all the available inventory for the New York level, this is probably the best use of your influence. Just use all of the remaining boost on the easiest Street Thug level 3 (Corner Store Hold-up) and 6 (Auto Theft) energy requirement jobs on the street thug tier once you have used up the majority of your energy on your other jobs. They don't pay out the best money or experience, but if you want to level up fast, this can really help.
The third and (currently) highest tier of Jobs Rackets is the Shipping Company, which only exists as a way for Zynga to tell you to screw yourself; the reward for this tier (the robbing-defense-increasing "Political Favor") is unusable by people who actually have Rackets instead of Properties, since Rackets cannot be robbed in the first place.
Racket Timing[]
One thing that might seem counter intuitive but is extremely important is to be consistent about when you start your Rackets.
If you are 50% of the way through an 8 hour Racket and you just earned enough to invest in another 8 hour Racket -- Wait. Don't invest in the next 8 hour Racket until the first one has completed. Perhaps consider starting a 4 hour Racket instead, and swapping it for an 8 hour racket after completion.
This will allow you to keep all your 8 hour Rackets on the same timing interval. If you invest right away, you might find that you need to check at odd and irregular times to keep your Rackets going.
From a Racket Management perspective, the more Rackets that are on the exact same timing interval, the easier they are to manage.