I have a mileage plan with Miles and Smiles by Turkish Airlines, but recently I'm taking a lot of Lufthansa and United flights.
Currently I am using the alliance to reward me on these flights, but should I create a mileage plan in the different airlines or is Turkish and Star Alliance enough?
Usually, it is better to keep an account one member airline per alliance. This lets you get rewarded for most flights and will allow you reach higher reward and privilege levels faster.
This is also good way to reduce changes of points expiring since there is more chances that activity will occur within the period in the account. A few programs have no expiry, but most do, so you need activity to keep your miles alive.
There are a lot of factors that go into this decision.
The first rule would be to stick with the program where you do most of your flying since your primary airline benefits will be better than partner benefits.
If you visit other forums where such topics are discussed, you will find travelers usually only make the jump when they can make significant status in another program, and often in a different alliance as well.
Since Turkish, Lufthansa and United are all Star, you're probably best off maximizing you Miles & Smiles/Star status if Turkish is your home airline.
The best place I've found for such discussion is Flyer Talk.
If you want to go for as much award credit as possible The Points Guy is a great resource.
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