On a audiophile-quality music system, the speaker wires do have a small effect on the sound. But a HT system is usually not accurate enough and the sound is highly compressed, dialog-heavy and not played over-and-over again so that you would notice any difference if you swapped out speaker wires.
I recommend good oxygen-free 12 ga for all your speakers. A spool from places like
www.partsexpress.com is a great way to go.
If you have some highly-accurate music speakers, I would still recommend you start with the budget-but-good 12 ga. Get used to the system for 3-5 weeks, then 'audition' more expensive cables and do your own A/B comparison before investing in a complete set.
I also recommend the 10% rule: Budget 10% of the price of the items you are hooking up for the wire. Spend no more than this or you are over-spending (but making some salesman very happy).
