
Advantages to rudder steering: Most comfortable position on a sailboat. Sailboats respond best to their rudder when underway. You can steer while coasting in neutral. This is the simplest setup.

Advantages to motor steering: Only the motor can change a sailboat's direction when there is no headway. The motor's controls are under hand.

Advantages to tying the motor and rudder together: You can get the best of both worlds for steerage and turning the motor and rudder in tandem can avoid rudder/propeller clash.

Disadvantages to tying motor and rudder to together: added complexity, harder to reach motor controls while steering.

Disadvantage to motor steering: Need to tie rudder down. No steerage when coasting.

Disadvantage to rudder only steering: Need to tie motor down. Difficult to reach controls. No steerage without headway.

Things to consider: Propeller and rudder swing, propeller guard. Ease of tying motor and rudder together. Getting remote or cabled controls for motor.
I would suggest moving from simplest setup to more complex as needs dictate. Lock motor and steer with tiller. If you find situations where that is not working, lock the tiller and steer with the motor. If you can steer both at the same time in comfort and still see where you are going (That seems awkward to me) try that. Then, if you still feel it might be worth the effort and expense, connect the two together. Buy or rig remote controls if you need them.
If you go with the locking one and steering with the other option, you may want to be able to lock either/or so you can quickly change over to take advantage or the different strengths as the situation demands. Look into a propeller guard so you aren't buying new rudders and propellers all the time.
-Will (Dragonfly)