Isofix or no isofix carseat?

Mi

Ok so originally i wanted a 3 in 1 travel system where you can click a car seat on the stroller cause i thought that might be handy (the car seats are usually generic ones you have to fixate with a seatbelt). Now i checked on car seats and came across the isofix which might be more secure then just using a seatbelt. My question is do you have an isofix car seat or a normal one you secure with a seatbelt and why did you chose for that?