I agree with you on the Tank. I also like the Americaine better than the Francaise.
There are a few things to consider when deciding which to buy, especially if you are looking for just one:
While both can be dressed up or down, and are versatile enough to style in different ways, I would say that overall, the Panthere has a bit of a dressier, daintier vibe than the Tank. Which one fits you better depends entirely on what you usually wear.
Also, what do you have in the way of watches already? Which of these would better fill out your watch wardrobe and offer you something you don't already have? For example, I personally adore the Panthere and very seriously considered getting it but ended up getting an Omega Seamaster Aquaterra instead when I realized that I already have quite a few dressier watches while I did not have a quality sportier watch, so getting the Panthere for me would not have offered anything really new to my ability to accessorize. For you, it may be the opposite.
Does the leather vs metal band make any difference to how it will work with your current wardrobe? Do you have a preference for one over the other with how they feel on your wrist?
Metal bands tend to last longer than leather.
Both dials are pretty small to look at, so if you have any trouble seeing up close, you will definitely want to try them on in person to make sure they aren't too small to read clearly.