This is a great country and our hobby has many fine mail order options. The quality of customer service is exceptional. I use all three of the original poster's choices and have had generally good experiences with all three and would buy from all again. There is a thread in the sponsor's forum about Bulk Reef shipping costs. The first thing you will notice is most of the critical posts are by the same posters who have jumped on them here. Same names and same issues. Bulk Reef have responded in that thread with great courtesy and patience. Most of their issues were also answered. With the exception of F&S, I think BRS shipping costs and policies are on par with other smaller retailers. My question is why these same posters are so eager to smear a good company. If shipping from a particular company doesn't work for your situation, find another source.
As to the OP's original question. Here are my thoughts.
1. F&S-good customer service. Hard goods [F&S] customer service reps. are polite, professional but have little specialized expertise with salt water/ reef issues. Live Aquaria/ Diver's Den CS reps. are a very knowledgeable about live stock issues and great to work with. I have problems with USP in my area and the company has gone to great lengths to try to remedy the local issues. Shipping packaging from LA/DD is beyond great and is the standard on the industry. They also use PLENTY OF WATER and larger bags which means more costs to them and healthier animals. The over $49.00 purchase free shipping is great and they are my source for salt. However, other hard goods products are not always packaged professionally. I ordered a 29 gal aquarium package to use as a QT. It took 4 tries to get one not damaged by UPS. This was mostly a UPS local issue but F&S shipping did not help as the shipping container was two card board boxes fitted together and taped. The interior contents were not secured with packing materials and rattled around. Their customer service was very good, promptly replacing and issuing a large discount each time. However all efforts by customer service to get the aquarium packed with more professional materials and methods failed.
Marine Depot- a good company better now they seem to have reduced their fixation with hobbits and fairies in their shipping notices! Customer service reps are knowledgeable but some have what I call the California attitude and seem to be a little abrupt for my tastes. This is a SMALL quibble and would not prevent me from buying from them again but I might go elsewhere for advice. They do have a large selection of reef related things and I enjoy their catalogs. They seem to have a early cutoff time for same day shipping and shipping time to me is a little long. It is not their fault. It is simply a function of distance. I find their shipping costs slightly lower than BRS but, on the whole, their prices slightly higher. I understand they will price match but the difference was never important to me. Like F&S, they sometimes accept an order for something out of stock. This locks up you order since you have already paid for it by the time you find out it will be delayed.
Bulk Reef- Exceptional Customer service and ALWAYS knowledgeable and patient. Great prices on RODI and Bulk materials. Competitive pricing on other items. They are small enough to be flexible and have even suggested I NOT buy a certain product they carry. Have steered my to home improvement stores to purchase items at a lower cost. I believe they use your phone number to see you buying history as they all seem to know me and will ask how something I purchased is working out. They never accept an order for something out of stock. Allows you to find it somewhere else if speed is important. Best same day shipping in the industry. Packaging very professionally done. Returns handled promptly and in a professional way. They have become my "local fish store" since the nearest decent [and very limited selection] is around 150 miles away. Great videos with honest presentation of products. Because of my location shipping is lightening fast. Ground takes two days. Order on Wednesday and get it on Friday. Times will depend on your location. For me, this is my first choice for hard goods.
Sorry for the length of this post but I wanted to give a fair, complete assessment. Kinda of suspect the venders may be looking at this as well as our members.
My final advice is for buyers look for a long term relationship with a vendor and throw that business the bulk of your business. That relationship will provide the buyer many benefits over time.
RJ