Alatreon in Tri was the coolest, most fun, most diverse monster ever, at least when you fought him alone. Comparing him with the older Elder Dragons is kind of difficult seeing how he's three times as big, faster and has his head out of reach for nearly the entire battle.
Don't know about P3rd. Like everything else, he's much easier.
What I have to say is far too important to fit in a simple textbox with a 160 character limit... Plus, I just wasted more than half of them by writing that!
The coolest monster is a squid can fly and be called "Elder Dragon" O_O
You mean the Jellyfishdrome that was a secret boss in Tri?
I think he meant the Yamatsukami.
FYI Elder Dragons are not classified by their appearance. Instead they are classified by their uniqueness, as in they don't fit into any of the other monster classes such as wyvern, bird wyvern, brute wyvern, pelegus, etc. Also each ED possesses different traits that are entirely unique to its kind and therefore most EDs are of different species, although some have shown to have a sort of relationship to another(e.g. teostra and lunastra). This is the reason why a thunder unicorn and a giant floating octopus/squid are also considered Elder Dragons.