Head to head
Which one will break you first?
Two fingerprints on one grid. Both are scored through your profile, so this answers the question for you rather than for the average player.
Stellaris is the harder of the two for you, by 0.8 points. The gap is widest on reaction, where Age of Empires II: Definitive Edition asks considerably more than Stellaris. If you want the gentler run, start with Age of Empires II: Definitive Edition.
Axis by axis, biggest gap first
STELLARIS
Hundreds of hours of interlocking systems with a mid-game crisis on a timer. Most losses happen fifty in-game years before anybody notices them.
Long walls, many attempts. Bring patience.
AGE OF EMPIRES II: DEFINITIVE EDITION
Build orders are the curve, and the campaigns teach almost none of what the game actually asks for. The hard AI does not forget its economy while it fights.
Sustained pressure. Progress is earned.