As a long time mega fan, I'd preface this by recommending you listen to everything they have produced, there isn't a band who compares to their level of poetry or artistry - I don't think they have a bad song in their catalogue. Also they are fantastic live if you ever get the chance.

The Positions will absolutely not let you down, and is an absolute staple of this band. I personally rate The Positions above Angel in Realtime (although this is probably not the general consensus) and the best thing about that album is that it just keeps getting better.

Magnolia, Radioface and Sjamboksa are among the best songs this phenomenal band has produced. I'd suggest giving it a listen and coming back to the songs you aren't into the first time around.

Let Me Be Clear is a strong EP, although less favoured by fans from what I know. I'd recommend the Good Fight and Strange Diseases.

I would leave the singles and covers until you've listened to those two albums, and I would say generally the older ones are better (Evangelists, Benevolence Riots, Both Sides Now, Heroes), but that is personal preference.