A4 question

First off, Sup im new here, and currently looking to buy an AUDI!!! So after doing some hw... I NOW know that the 1.8t (A4) is better than the 2.8l... But still have some questions. Im buying a used an i saw that practically every year has some engine issues. So i need to know what year is "gold" and if the 1.8t and 1.8t quattro have any difference (besides one being AWD and other being FWD??) and any thing else a first time audi owner should know...
Thanks guys