Can someone give a thorough explanation as to the difference in buying altcoins with bitcoin, etherium, tether, ltc etc.

I have been purchasing alts with bitcoin on btx.  However I have read a few posts on reddit saying you should use ethereum to make purchases and NOT bitcoin.

Can someone explain the differences in purchasing with different methods?

pros and cons, if there are any?

If there is cost implications?

Your valuble information wil be greatly appreciated