The huge benefit of OSH Park is that all boards have a gold-plated finish and a sweet purple silkscreen
Just received an order from Seeed myself, 21 days from placing the order to receiving the boards in North Carolina with the cheapest shipping option. The boards look good, and they gave me 12 rather than the 10 I ordered. There's no need to add the order number to your Gerbers any more, nor to e-mail them in--they now let you upload them on their web site.
For boards smaller than 5cm x 5cm, such as tiny breakout boards and adapters, I go with OSH Park. They charge $5 per square inch for 3 boards, free shipping, so if your boards are very small you can expect to pay less than Seeed. The huge benefit of OSH Park is that all boards have a gold-plated finish and a sweet purple silkscreen -