Welcome to the worllld of mac!! It all depens on what you're looking for, what kind of colours/products. My top 5 favourites are:
Vanilla pigment - great highlight, so easy to play with!
shroom e/s - a natural, but I use it almost everyday!
Humid e/s - Green, Gorgeous gorgeous if used with juxt!
Blacktrack fluidline - liner, a really great gel one too!
studio tech foundation - best one i've ever used, so light and easy to blend, I wouldnt recommend it on some skin types though, ie dry it may make it look worse.
Hth!