GHL's killer feature is white-labeling. As an agency, you can run unlimited sub-accounts under your own brand, charge clients monthly, and bake in your own margin. No other platform on the market is structured this way at this price.
Kartra is the better answer if you're not reselling — cleaner UX, easier learning curve, more polished funnel + email tools. It's not white-labelable, and it's not trying to be.