Best infant car seat?

I am going with the uppababy stroller and so it has to be compatible with adapters. I have a britax but there is no britax uppababy car seat adapter so looking for a new infant car seat. I love my maxi cosi convertible car seat that my son now uses but not sure about the maxi cosi infant ones? Also the weight limit on the britax was 35 lbs but he outgrew it by like 20 lbs hes broad and his shoulders where squished so wondering if i should skip it all together since its like 200 something dollars for a few months use. I could use my britax n then just get a convertible when shes too big. But then i lose the convenience of a car seat travel system. What are you mamas doing?