I think the plastic is easier to see through or around. I find the ones which are closed toe (the thread has to come up through the center of the foot, not at the front of the toe), are a royal pain. But I am a beginner.
I also don't like the ones the bounce up and down at every stitch - you can get a Janome adjustable with multiple springs but the whole foot doesn't 'hop'.
Good luck and have fun with it!