Your opinions on how to string 25 ft speaker cables

A slight twist may help keep them together and be a practical solution for installation. 

As as far as the sound goes - twisted or not - it is irrelevant for speaker cables.

I do not think there would be an audible difference at speaker level.  I do think that it will be easier for you to just pull the cables as a single bundle, rather than to twist them.  

I agree with Kijanki that twisting cables reduces emf effects and such, but you don't need to be too concerned about that at speaker level as the signal level is already so high. 

I work in the professional ,audio world and have been involved in many very high profile projects through the world.  I have never seen anyone twist individual speaker  wires, especially if carrying different signals together.

+1 richz.
If you should decied to twist don't forget that the wire length needs to be a bit longer.

I'm running a similar setup with similar cable, except with 2 less cables:  basically two 24' runs of 12 gauge AntiCables under the floor.  Speakers have only one set of binding posts, so this is just a true "double-run" of cable.  I went to the effort of trying this 4 different ways: cables run simply side-by-side in a "shotgun" type configuration (both conductors of one cable to the "+" terminals and both conductors of the other to the "-" terminals), cables run side-by-side in a typical bi-wire configuration ("+" conductor of both cables to the "+" terminal and "-" conductor of both cables connected to the "-" terminals), and then both of those configurations with the cables twisted together (one full twist about every 6").  Very obvious difference for the better (in this setup, and to my ears) with the bi-wire configuration -- the "shotgun" setup seemed to be a touch smoother on the top end, but robbed initial attack on transients and curtailed overall dynamics to a very noticeable degree.  The presentation got boring, if you will.  I did not notice much difference with either configuration in the twisted versus untwisted configuration.  As the twisted setup was my last trial, I just left them twisted and did not go back and untwist them for a final verification.  Happy enough with the result in that config. And the addition of the second set of cables was a very nice improvement overall -- more dynamics, more (apparent) extension in the bass, and more depth to the soundstage.

What 12 AWG cable do you have from Monoprice? Is it the clear or one of the CL rated ones that have a red and black in an outer jacket? IMHO, I would not use the clear in a crawl space.