Bookshelf or Surround Speakers as Surround Speakers?

We get this question a lot and the answer is almost always to go for the Surround speakers. 

For the most part, our TriAxial surround speakers are direct-firing. Like a wall-mountable shallow bookshelf speaker if you will. But in addition, they use two small 4" (3" in the 1961 Series), full-range drivers on the side in dipole mode from 200Hz and up.

This creates a much greater envelopment and wider sweet spot, compared to your standard bookshelf speaker. All of this is achieved without losing any detail or directionality.
This design can be extremely beneficial if you are sitting close to the surround speakers.
Normal monopol speakers will struggle to create a sense of space in close proximity, as they need some distance to give you the soundstage you expect. Basically, the same rules apply as with your front speakers.

As a bonus, our 1723 Surround and 1723 Surround (S) offer the option to operate in standard monopol mode.
By just disconnecting the jumpers between the terminals and hooking up the speaker wires to the lower binding posts you can decide what sounds best to your ears.
A very versatile speaker that can be used in a variety of setups.

To sum up, choosing the right surround speakers will mostly depend on your room, speaker placement options, and of course, personal preference.