I’m a car seat expert by trade (I run car seat libraries uk, although not so much now thanks to Covid 😡) - the maxi Cosi is lighter, but the Cybex lies flat on the pram. So if you’re going to be using the car seat on the chassis a lot, then go for the Cybex. If not, you may prefer the lighter weight of the maxi Cosi.
In terms of crash safety, both are excellent.
A benefit of the Cybex is the rotation infant seat function - handy if you have back issues after birth and also if you have a section.
The Cybex also lasts longer. It goes to at least 18m (depending on baby of course). Maxi Cosi goes to 12 months max.
Both take the next stage seat, the Cybex Sirona z rotates, maxi Cosi does not. However I wouldn’t let this sway your decision - the compatible next stage seat may not be the best option for you after the infant seat, and if you plan a second baby, then you end up needing another base or having to move your first up yet again very soon. There is a massive host of options for toddler seats, including extended rear facing 25kg seats that you may wish to research.
On a personal note - I have opted for the cloud z for baby due in April.