Most certainly the Cartier...the tank is such a classic, you can never go wrong with it. The others are nice, but I think the Tank is so much more iconic and lovely compared to the Baume and Merciers'. Cartier hand polishes all of their cases, and has very high standards for their watches, and I think they are just another level as compared to the B&M's (Baume and Mercier is much more a pseudo-luxury watch brand and Cartier is a true luxury watch brand, IMO). The Cartier watch would also keep its value much better than the B&M if you decide to part with it (which I am sure you wont because it is so beautiful!!!).
Summer - for under 4k, you might want to consider JLC Reverso Lady quartz, ss, leather strap. Or the Omega Constellation Quartz 35mm ss, leather strap with diamond markers. Cartier's Tank Solo looks classic. I don't like B & M. Better off with Longines's Primaluna.