Have never touched either boat. Best advice I have is to try and trial sail both of them. However, if not possible, you can try to add some engineering results to any opinions expressed here.
1) Sailboatdata.com is the worlds largest sailboat database.
You will need to find out the particulars of that catalina.
The Aquarius 21 is not one of the built in choices. You will need to enter the data from (1) into the calculator and then select the catalina to compare with.
The web page has basic information on how to interpret the results. Other than performance and engineering factors, the Catalina 22 is one of the most popular boats. Lots of support and spare parts (used or otherwise) out there. I don't know about the popularity of the Aqu.