For the most part with regard to size and grip, a 1911 is a 1911. If you only want to hold one to see if you're comfortable with the fit, find any 1911. There are few models to compare to if you're interested in the double stack versions.
If you like the 1911 style, you will love the STI. The fit, finish and smoothness of operation is second to none. These fine details are the differences you will notice with the STI. Of course, along with that you'll notice the price tag but rest assured they are worth the extra price. The entry level Spartans are a steal for $700 and I can't figure why anyone would buy anything else just to save $50-200.
If you really want to see why an STI is a fantastic pistol, find someone who will let you shoot their's. Just don't start with the Trubor GrandMaster or be prepared to eat KD for a while.