Find myself playing arty a bit more. Any recommendations of which path to take?
As Munk says I love the SU-5!
The SU-5 Soviet SPG, (Tier 4), is a pure and simple joy to play once you get the 152mm Mortar. Even with only 14 rounds it can hit targets hidden behind cliffs and buildings. It's got an insanely fast reload and is accurate as hell. I found the next one up the SU-8 disappointing in comparison.
I've gone French also and I'm up to the AMX 105AM tier 4. They are quick, but don't have the fast reload of the SU-5, (what has?), but are accuratish and have a good range and damage. The Lorraine is great at taking out tanks outside of Arty view and doubles as a TD.
The German ones are powerful, but slow to load. The Bison is great the Sturmpanzer (sp?) not so.
Not tried the other Nations yet.
My plan is to max out the French line in SPG's. I'm staying at the SU-5 in the Soviet line - it is my fav beast in WOT.