It could be the fact different companies have similar yet not quite size charts? It could explain why your fit with the Marin and Safire weren't same.
Switching brands can be quite a factor to satisfaction and usability so to speak. It's just a transition period. But that aside, if you do go for a Safire, make sure you're actually comfortabel with it and see yourself going with the fit for it long term.

Trust your gut feeling. It helps. Women have a strong sense of intuition. If it feels wrong, don't do it.