Spinner size and shape is determined by the plane, and by your preference.

I prefer aluminum spinners but use nylon on some models (I prefer the price of nylon). I've used nylon spinners (with nylon backplates) on .61 two strokes and ,91 four strokes with no issues other than I dislike having to custom cut the slots. I do it but it is not something I enjoy.

If your plane has a cowl, you will probably want to choose a spinner that blends nicely with it.

If you do not need to match a cowl, it is 100% YOUR preference. Tru-Turn makes "wide blade" spinners in many shapes and sizes. This page shows samples of the shapes that are available. http://www.truturn.com/Spinners/By_Shape/by_shape.html

This link is to a 2.25 inch 'ultimate' spinner with wide slots. I like the pointy shape of the 'ultimate' design. You may hate it.
http://www.truturn.com/cgi-bin/store...exact_match=on

There are choices other than Tru-Turn, they are just the one I have bookmarked on this computer. Tru-Turn will custom cut any of their spinners to fit any prop. I think Dave Brown Products will also custom cut their spinners to fit any prop.

Again, if you are not trying to match a cowl, or a scale shape, pick the one that looks best to you because your opinion is the only one that matters when it is time to spend money.

Maybe you do not need a spnner at all. I really like aluminum or brass prop nuts for planes that do not need a spinner. Here are a few examples that will fit a 75AX
http://www.truturn.com/cgi-bin/store...exact_match=on
http://www3.towerhobbies.com/cgi-bin...?&I=LXE192&P=0
http://www3.towerhobbies.com/cgi-bin...?&I=LXK242&P=0
http://www3.towerhobbies.com/cgi-bin...?&I=LXL731&P=0
http://www3.towerhobbies.com/cgi-bin...?&I=LXCC41&P=0