I took mu aluminum bike for a 25 mile ride on an island with less than perfect roads and the road vibration really got to me, as well as my upright position made me feel like a sail in the wind. I believe that steel absorbs road vibration better than aluminum. I have not ridden, nor was I interested in carbon, so I didn't test ride any of it.
My best advice is to educate yourself about bike geometry, sizing (this is a whole long topic in and of itself), and componentry. Do a lot of test riding and when you narrow it down do longer test rides. Is it possible to rent bikes where you are? That way you could really do longer rides on different styles.
Also, and I'm just throwing this out and it may not apply to you, but just because one likes spinning classes does not mean that will translate into loving actual outdoor riding. Just a thought. Make sure a bike is what you really want especially if money is a concern.
Also, do you plan to race or simply do recreational rides? Is commuting by bike in the cards? If so a bike that would allow racks, fenders etc. Might be appropriate (many road bikes are not equipped with the ability to have racks, fenders, etc.