The two are for all intents and purposes completely interchangable with a release pattern that is almost identical. Worldwide, Test Enanthate is highly available and probably the most popular form of Test used by Athletes. The only caveat to the aforementioned statement is that Test Cypionate seems to be almost exclusively American based and for that reason is much more widely prescribed here in the U.S.
Test Enanthate = 72mg of Test per 100mg of AAS
Test Cypionate = 70mg of Test per 100mg of AAS
Test is test, so get whichever is cheaper bro. If you don't mind ED or EOD injections, you will actually get more bang for your buck (Test) with Propionate or Suspension. Most people prefer a much more comfortable dosing schedule, hence the development and popularity of the longer esters such as Cypionate and Enanthate.
Cyp is heavier(more oil) and has slightly slower release point than enth
But Cyp is less concentrated than enth relatively speaking. Cyp seems to be prescribed more because some ppl take an injection every 2 weeks. From experience that's a difference of about 1-2 days from cyp to enth in how I felt them. In my book it does not matter but from HRT stand point it does make a slight difference. Either one will do in a cycle though