I havnt had great experience with online. But here are some super easy corals.
Palys
Duncan
Leathers
Mushrooms
Galaxia
Most lps
Montipora
In my experience......
Legendary corals is great but they deal in high end collectors pieces. Not bad if you can catch a live sale like they have right now but otherwise a bit pricey for the beginner. I will be honest somehow someway you will loose a coral during your reefkeeping career. Wiz has a good list going. All of those if they are not priced super high are going to be tough and grow good for you. I recommend getting corals from others on the site. Most would be glad to help and these corals are used to captivity.
I have from uniquecoral.com and have had a great experience (Zoa, and Xenia with a few others). Have also got some from Saltwaterfish.com (frag packs) which ended up a 50/50.
Question I'm wondering is if anyone has any idea about limits on how much coral you should or could put in a tank. Fish you have the inch/gal limits but I have never found anything about coral limits.