Gujranwala bypass is horrible. The so many round-abouts (chowk) on bypass (Awan chowk, alam chowk etc) are the main culprits of traffic jam. Travelling through the city is still better. However, you will find traffic block at few places, especially the traffic signal at DCO Office (if I remember correctly).
GT Road condition is mostly good especially I love the Jhelum to Gujrat section of GT Road but there are some rough patches near Muridke, Komoke.
If you do decide to travel via GT Road, get onto M2 motorway from Kala Shah Kaku (after Muridke). That way you will be able to avoid really bad traffic jam near Shahdra and onwards (that place is still under construction). From M2 you can easily enter lahore via Thokar.