Re: NextWorth VS Gazelle for iPhone 5 trade in:
I recommend NextWorth to trade-in your iPhone 5. They offer the highest value making it easier to upgrade to the 5S for free. Plus, NextWorth offers a 30 day price lock so you can hold on to your trade-in until you receive your new device. I understand your uneasiness with the online reviews, but often people that love the service aren't necessarily the ones writing the reviews. Check out the following links for more information on NextWorth's iPhone trade-ins:
Also, let me know if you have any other questions. I've traded in with NextWorth a few times (and so have my friends). We'll always been happy with our service and the money we get from the trade-in.