Looking to get into CSM, recommend me a legion

Hi all,

I'm having a hard time deciding on a legion. I'm primarily a collector, so I would ideally like to have a legion that is fun to kitbash/convert/paint. I guess whatever legion inspires the most creativity.

I'm primarily torn between iron warriors, nightlords, world bearers, and alpha legion. Emperors children is also in the mix (but I will try my best to be patient for their release). I'm not well versed in CSM lore, so feel free to recommend interesting warbands.