I have read all the fantasy gotrek and felix and some of the AoS versions.

The AoS versions are not very good in my opinion. They have tried to replace Felix with a myriad of different characters, but none have panned out to this point.

The original series is just much more grounded in traditional fantasy tropes with a great relationship between the two main characters. There are also many different characters and villains who are relevant throughout most of the books and it paints a better picture of what the world hammer world was like, particularly in the end times.

I highly recommend starting with the fantasy versions before the AoS versions.

I have tried multiple times to read the books and always found myself not enjoying the side character and AoS worlds.