Unfortunatley, I've found a difference of at least 1 size is common across brands. Also, look out for "race fit" stuff , which will be even smaller. Best way is to be able to try stuff on and/or return it.

I personnally like a little extra size in the jersey, especially for group, training rides. It's just more comfortable and doesn't really cost much in terms of aerodynamics, etc.... On the other hand, shorts that are too big can bunch up and be problematic.... but there is a lot of preference involved here.