I do agree with some, the 550 and the 560 to an extent are different beasts. Its like comparing Arnold S. [550 imo] vs Slyvestor Stallone. [560].
The 550 is nice, great size [a more legal size in mind], very compact - like a brick, tough, and in this regard a real tank. Thick blade, thick handles, solid lock up. Some have issues with flicking it with the thumbstud, but it does get easier after time.
The 560 is a sensational experience. It feels great flipping and letting close [as well as sounds great

], the handles are machined amazingly [much preferred vs the dgg strider handles for me - the dgg is a bit too rough and the 560 is a perfect medium imo] - not to mention the contouring helps fill in the gaps in the palm for me. It has harsher jimping on the lock + top for most, but I am fine with the roughness. It allows calluses to form and it doesn't hurt any more for me

plus they soften over time. Super smooth and quick, solid lock up great blade geometry. It is "thinner" than the aforementioned, and skeletonized to an amazing extent, and with amazing balance.
To better answer your question, answer these questions for yourself.
What is the knife for? regular edc? harder use edc?
Are you comfortable with carrying a blade length of the 560 size vs the 550? [ex. do you feel comfortable knowing it may or may not be legal to carry]
Do you want a flipper + thumbstud, or just a thumbstud?
Do you prefer to have a quick deployment with flipper and thumbstud? Or a quick strong flick of the thumb + controlled opening?
Do you want a base heavy knife [550, compact weight] or do you want a more balanced knife weight wise?
What kind of blade thickness do you prefer? One is thinner, slightly better slicer imo, while the other can be used for a bit more work.
If you notice, those questions are one or the other [550 or the 560] see how they total

And feel free to add questions.