You will get a million different answers here as everyone has their favourite! In general, LF lenses are quite slow compared to what you have been using, ie around F5.6 is the norm. There are thje Zeiss Planar and Schneider Xenotar at F3.5 in the 135mm focal length, but these are hard to find and expensive when you do. If you are doing portraits with say a 210 or 240, then the DOF is still pretty shallow at 5.6 so it may be OK. I personally use a 270mm Schneider Tele-Arton for portraits. The 210mm lenses seem quite plentiful and anything from Schneider, Rodenstock or Nikon will give top quality images.
Unfortunately I only shoot B&W, so no idea of colour rendition I'm afraid! In my kit I have a 180mm Rodenstock Sironar and also a 150mm Sironar, both these lenses have particularly pleasant OOF areas, so could work with portraits.
A lot of people here use really old lenses for portrait work and some of these produce amazing results, but I'm no expert here as the only oldie that I have is a pre-war 210mm Tessar, which is uncoated and really nice wide open.
Really like the snow pictures you have and the second shot is a good example of where LF could improve your image. By tilting the lens forward you can easily get good front to back sharpness in pictures like this without stopping down drastically. Good luck with your quest and I hope you like LF.