I have a bit too much steering but it's close. If I were to adjust one of these features on my Futaba 4pl, which is better? Servo speed or steering EXP? What is the difference? I am looking for smoother transitions.

Change the expo. If you change the speed and get in a jam you can't make it go any faster. If you are using expo all it is doing is lowering the resolution around center, if you go to the end point quickly it goes at full servo speed..

I find both to be useful tools for changing track conditions or even temporarily masking a failed setup attempt.
If you often turn from lock to lock, like on a tight or fast track, slower servo speed can really help to get you a smoother transition.
If you are constantly turning in small amounts then expo is a better adjustment and can really tailor the steering curve right where you need it.

Of course neither of these adjustments will reduce total steering at full throw, 1 or 2 percentage points on the dual rate can go a long ways at making corners easier, but could get you in trouble in tight sections.