I've done 5 mythic dungeons at this point and all my characters are around 440-445. The 5 I've done, in order of difficulty from easiest to hardest:

MOTHERLODE - This was stupid easy. I think I only wiped on one boss and did 0 looking at abilities prior to attempts, just did it live. There's a bit of luck involved on the first boss with bomb placement, but I just use my speed boost to grab them.

Freehold - I hate the trash to the first boss, and the first boss is probably the hardest from a mechanics standpoint, but is otherwise really easy.

Tol Dagor - Nothing really stood out as difficult or easy. Last boss was a challenge, I kind of just zergged the mechanics which will hurt me in the long run I'm sure.

Waycrest - I'd consider this slightly higher in difficulty. It's not difficult but some of the bosses are kind of annoying and the mechanics become a bit of an execute.

Temple of Sethraliss - Probably tied with Waycrest. There are some really easy bosses, there are others that require a little bit of execution, but overall not super difficult. The event prior to the last boss is really annoying. I have 2 keys for this, this week. I don't think I'll have time tonight but I'd like to make an attempt at the +2. I feel like I'll probably miss the timers just because I've only seen the mythic mechanics once thus far.

I did clear 3/4 out of Shrine. Each fight (aside from the first) was pretty difficult and required good execution and an understanding of mechanics. A far cry from impossible. I didn't spend much time on the last boss but I know it's going to take an hour or two of wipes to finally get it. I did have to spend an hour on each of the 2nd and 3rd bosses.

Lyonheart - I thought I saw you saying in another thread you're 440ish, if that's the case, you'll probably mudstomp at least one or two of the above dungeons.