My "go to" company is Classic Industries without question. They are typically cheaper than Year One on specific items and have far better customer service.
I do, however, shop around for price, most of the time. In the last 20 years I have amassed a good list of vendors that offer top quality, American made parts with quick shipping, and have been able to save quite a bit of money and still get high quality parts. It just takes a little more time.
I cannot in good faith recommend a company or service that I do not have confidence in. I have bought my share of parts from Year One but don't particularly care how they do business. It seems that the generic items are always offered for the discount but other, more specific, have-to-have parts are always discount or free shipping exempt. Also, they do not make it clear what they have in stock or not, or make any effort to notify you when it might be available. I have waited months on some items that obviously were backordered, and have been paid for, with no correspondence what so ever as to the status of the order.
I value good quality parts, fast shipping, and good quality customer service. That is what I have considered in assembling my list of vendors. But that's just me!