My thoughts are primarily to buy local. Probably doesn't really matter where exactly, just somewhere you can get to easily. That way, if you wind up with a defective unit, you can easily take it back for a new one within the return period.
Some places have their own loyalty card things. Best Buy has its reward zone thing, where for every so many dollars you spend in the store, they'll give you a coupon for $5-$25 off some future purchase. GameStop has something kind of similar. Think they call it an Edge card. It gives you a little extra in trade in values for games, and I think a small discount on used games, but there's a monthly fee associated with it, so you really have to do a lot of game buying to make it pay off. I'm not really aware of any other stores that have anything like that.
Promo deals are going to be region and time specific, so you're on your own there.
And as for customer service... I'd have to give a hesitant and slight nod to GameStop. If nothing else, the employees typically know a bit more about gaming than your average clerk at any big box retailer. Though they kind of run the entire spectrum. Some of them could teach a used car salesman a thing or two about high pressure sales pitches, while others seem to really only care about what time they get off work. Most of them are in the middle though. Fairly passionate about gaming, will suggest things, but not really pressure you.
If you happen to have a membership at some warehouse club like Costco, Sam's Club, or BJ's, those places tend to pile on the extras. Microsoft and Nintendo mandate the price they have to sell the console for, but a lot of times they'll toss in 2-3 games, an extra controller, and some other accessories for "free". They also tend to have the most liberal return policies. Just don't expect any help picking things out.
Still, no reason you can't buy the system at one place, and then games at another.
... erence?
Gonna get either a Xbox 360 or a Wii. And please, I'd like this to be a discussion on WHERE to buy these things, NOT which of the 2 console systems to get. Push come to shove, it doesn't seem like there's any difference on where you get your stuff? My main preference would be to get new products (maybe not so mcuh with games and certain accessories) as cheap as possible.
COST
Unlike other items like books, board games, or certain generic consumer electronics, since almost everywhere sells them at the same MSRP, it doesn't make a difference AFAIK.
LOYALTY POINTS:
Do places like Gamestop have this? Something like buy 10 games, get 1 free
PROMOS:
I hear Sears (or was it Target?) gives you 2 free additional games (Call Of Duty) + other accessories when you buy an Xbox 360. Don't have the ad, but I hear they're not charging you more for those extra things (which would nullify any savings, of which this I hear is around $60). Wii used to be $200 + get a free $50 gift card at Walmart back around Christmas, but I wasn't around for that.
CUSTOMER SERVICE:
someplace that's good about helping you than pushing sales. Also, have some decent exchange/return policy.

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