Here is my experience. Marine Depot has been perfect for me. No problems ever what so ever! The Drs. Foster and Smith, I have had a problem more than 50% of the time with them. Both on the dry good end and live. The only thing that I can say about them is that they are lightning fast at responding to my emails about the problems and solving them.
I've purchased a fair amount of both live (liveaquria.com) and dry goods from Drs Fosters and always had good luck with them. The few times I have had problems, their customer service is a model all companies should be looking to replicate.
I once ordered a Rose Bubble Tip Anemone that I lost in the first 8 hours to a powerhead. I wrote to Drs Fosters telling them about it, clearly it was my fault, I was just looking to possibly get a sympathy discount if I ordered a replacement right away - they gave me full credit on it despite it being my fault.
I prefer to give the business to the local retail fish stores, but you can frequently find things online that you just can't find in the local stores and/or get items at monster discounts. When that's the case, I have no concerns whatsoever about purchasing from Drs Fosters (LiveAquaria). For what it's worth, I've also purchased from Indo Pacific Sea Farms and Marine Depot and while I have no specific complaints of any serious magnitude, I didn't feel the quality of the goods, value or customer service was even remotely comparable.