I used to use Newegg for all my computer parts from 2001-2012. Their website was the most organized and easiest to find parts.
However, after 2012 I have ordered some parts from Amazon (probably 50/50 Newegg/Amazon.
I tried out Jet, but I was unimpressed with how their partner companies packaged the parts I ordered ($200 CPU in a plastic bag, no padding and a motherboard that was shipped in a flat rate box, no padding and arrived damaged with a hole in it).
The only issue I had with Newegg was reaching a person when a case I ordered last November was delivered to someone else. I tried the online chat, and it estimated an hour and half until it connected me to an agent. I then tried just to send them an email, but I received an auto-reply stating they were busy and might not respond to emails for 7-10 days and suggested I call or use online chat for quicker service. Long story short, it took me around 2:30 - 3:00 hours on hold until I got an agent on chat.
Amazon is good for me outside of sales tax and sometimes higher prices. I am a Prime member and many items I can have delivered same day if I order by noon. I do think out of all the companies, they have the best customer service.