I think the current top 3 hard-to-get are the following in this order (CRT may go in front of 'Ohana, but, at 180+10 days, I think it's 'Ohana):
Be Our Guest
'Ohana
Cinderella's Royal Table
To round out the top 5, maybe breakfast at Akershus or Chef Mickey's?
The closer it gets to the day of, I think the harder it is to get character meals like Crystal Palace & Tusker House - especially for those prime early morning times.
Le Cellier used to also be an "in demand" ADR, but, since both lunch & dinner are now 2 TS credits, I'm not sure if it still is or not.
For some reason, I also have problems getting the time I want for Sci-Fi in DHS. For the past 3 years, I've gotten an ADR but not for the time I want, & I'm making our ADRs on our 180+10 day.
Victoria & Albert's is also sometimes hard to get, from what I've read.
And, once California Grill is open again & taking ADRs, I'm sure it will be a "hot" ADR too!
As for our current favorites of the "hard-to-get" ADRs, we always schedule breakfast at Chef Mickey's, lunch at Crystal Palace, & dinner at CRT. For our upcoming trips, we also have an ADR for Be our Guest - I scheduled it first, & I only had 2 choices for times.
Be our Guest is definitely the top ADR right now.