I have ordered from Airsplat once before.  The items shipped fairly quickly and everything arrived safe and sound.  They have a great selection and low prices.
           I have ordered from Airsoft GI twice three times now and everything has gone very well.  While shipping wasn't the fastest, they included lots of free extras, checked my guns to see that everything worked well, and sent a chronograph confirmation slip.  They do not carry lower end guns for better or worse, so you should check out another site if that's what you're looking for.  Also, their selection isn't always the best, but you can request an item to be restocked, and their service is so much better than anywhere else.  Prices are sometimes a little high but they run loads of outstanding deals and codes all the time.  The best part is that they are the most reliable dealer I have ever bought from, and if the item is in stock at Airsoft Gi, that's where I'll buy it from.
           Once I have recieved items ordered from Airsoft Megastore.  Shipping was average and everything worked fine when it arrived.  I believe they may have sent extra BB's with my order for free as well.
           The selection is not the best, given that they are not dedicated to selling Airsoft, and prices may not be the best, but Free Super Saver Shipping is a great deal compared to most places.  On any other site you'd have to spend $75 - $100 to be eligible for free shipping, as opposed to $25 on Amazon.  They aren't good for getting AEG's and the like, but I'd say they're one of the best places to get accessories.