I ask the question: what periods in history and in what country interests you the most?Go for Mozart,Haydan(s) and then move on to Beethoven,Wagner,Bruckner in the 19th century.
Renaissance: Look for good choirs that do Palestrina,Byrd,Tallis,others. Also look for early music specialists such as The Tallis Scholars.They do it all.
Baroque: Again, period groups and better choirs. Bach, Handel,Vivaldi,Purcell to name a few.
After you zero in on the groups you like, look for other groups that are from the same philosophy.If you like Acadamy of Ancient music you will probably like The English Consort, and Concentious Musicas Vein.
good luck and have fun.
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