You will want your spinner right or center unless you are a lefty who also mouses left handed as well AND don't care if the other 85 percent of the population won't be able to control your game.
Right handed people usually have extremely poor fine control in their off hand and will find left handed spinners hard to control. Left handed people live in a right handed world and thus usually do quite a bit better with their off hand. They have been playing on controls designed for righties since they picked up their first gamepad.
Tron had it wrong, the controls should have been the other way around. I have a Cabal with lefty trackballs and right handed people find it extremely difficult to play.
I'm not going to push on this argument very hard, but ultimately,
it doesn't matter which side you put it on.
Neurologically speaking; your brain, and your hands, will adjust to whatever position you put it in after a couple of weeks of practice. Yes, of course, you may still have a "preferred" hand/side to play from, but you won't feel nearly as uncomfortable. Case in point; I have a trackball that is centered, with buttons on either side, and I am equally proficient with either hand. Granted, I'm not setting records with either hand

but neither position feels "off."
This was proven to me back in school for massage therapy (a profession in which overt single-hand dominance is a disadvantage) when our Neuro instructor tasked us with learning to brush our teeth with our non-dominant hands. It took about 2 weeks for it to become facile, and yeah I still "preferred" to do it right handed - but I can still do it leftie. I've been thinking about learning how to play Street Fighter with a right-hand joystick, just for fun.
Personally, I prefer the Tron layout; spinner on left, buttons and/or joy to the right - but that's just because I like Tron, and remember the layout. That said, I plan on having my spinner as close to center (along with the trackball) as possible, so that
other folks can conceivably play with either hand.