Hi Christophe,
I got the 5053 a few years ago when I felt it was the perfect calatrava. It is a fantastically beautiful watch and finished beautifully albeit a bit delicate for a daily beater. At the time, the 5053 had just been discontinued (I think about 2006?) and the 5127 was one of the models sitting around in the shop dismay cases seemingly a regular, not too special model. That made the 5053 seem all the more desirable. Also, SteveG's excellent review of the 5053G on his website (you can google for it) sealed the deal for me cos he highlights the 5053G's exquisite detail and finishing. Since then, I have acquired the 5053 in rose and white gold.
I let the 5127 pass but lately found it's really a rather handsome watch, with what I feel are nice proportions and of a nice 37mm diameter, which seems more contemporary. It was taken off the catalogue for a short while and put back on again the the PP seal and updated movement. I compared the 5127 with the other available and discontinued calatravas and decided to pick one up recently. One problem for me was whether to take it in the very classic YG or more understated WG. I finally went For WG. A close second choice was the updated ref 5296 with the plain (as opposed to sector dial). The 5296 is a handsome watch too with classic lines and contemporary proportions. The deal breaker for the 5296 was the all the 3 hands were a bit too short! Didn't seem obvious at first but once I noticed it, I knew it would always bother me so that watch was out for me.
Personally, I think you will be happy with either watch as both are fine pieces. I have put my money where my mouth is!
Acquiring a watch is a commitment of resource and time so careful consideration and garnering opinions is important. To me, buying indiscriminately takes away from the whole experience. This is a journey of knowing oneself and more than just knowing the watch. This journey also takes us to different places depending on where we are in life. It's fun and interesting. Unlike in marriage, it's ok to change your mind and to have more than one!
Hope you find this helpful.
Warmest regards
Doc