Nothing really except that you don't get lost in Start10 like you do in classic shell's settings.  With Start10 it is easy to set up, it does not make your head spin.

I have downloaded the demo.

I have to disagree with you both.  Over all Classic Start Menu (CCM) is far better.

CCM:  The setting window is plain and simple.  Very little scrolling up and down as the scroll windows are twice as big.

Start10: Spent to much effort on a pretty GUI.  confusing.

Start10 is really kinda confusing to use.  Some parts just dont make sense or are just plain hard to follow.

CCM has two view make changes.  Default (4 tabs) and "Show all settings" (13 tabs).  Nice.  Each view is setup is a very simple to follow tab format.

CCM also tracks the changes you make, so you know what you changed.  Nice.

Start10 the Control and Desktop dont even make sense as to what the options do.

Start10 if you hover over an option nothing happens.

CCM if you hover over an option a quick window shows telling you what the option does.  Nice.

Start10 only lets you hide the Search box.

CCH gives 14 options for the search box.  Plus you can hide it.  or you can just remove the "Search the Internet option".

I am not promoting CCM,  I am just pointing out that 4.99 Start10 is a waste of money seeing how it over all very limited as to what it can do and is confusing.

CCM is straight forward and easy to understand what the options do.

Fences is in a class by itself.  It is a must have.  Dont just buy one buy two.

To OP. By now you will have found arguments in favour of both Start 10 and Classic Shell, and you will have decided upon one or the other.

But for the benefit of other readers: I've tried both, and I won't attempt to influence anyone by saying which I settled for, but I will say I had a hard time choosing, as they both do the job admirably, it really does come down to personal preference. Price is hardly a factor, seeing that Stardock is practically giving it away, and Classic Shell really needs donation support. So my answer is: take the opinions with a pinch of salt, and try them both. As a result of doing just that, people will generally claim that the one they are using (whichever) is the better one, when what they mean is, it's better for them.