When it comes to 120 film you don't have as many choices with color film, or even black and white film for the matter. When you think medium format my tendency was to first consider slide films but the flexibility and cost savings of C-41 make it fit my workflow much better. What I look for in every film is versatility, consistency and value. And after 3 years of shooting various color films in 120, I've landed on Kodak Ektar 100 as my favorite color film for medium format.
It seems a bit counterintuitive that a 100 speed film would be really versatile but the thing that makes Ektar great is the ability of it to be overexposed 3-4 stops with little downsides. When shooting medium format cameras like Hasseblad 500CM and Rolleiflexes, I'm less inclined to make quick changes in focus, aperture and shutter speed. My favorite combination at the moment is to have a 50mm lens on the 500CM and keep the aperture fixed at F4 and shutter speed at 125. This exposes the shadow fine in direct sunlight and allows me to hand hold the camera. It also adds the risk of overexposing the film multiple stops.
With other C42 films like Lomography 800 pushing the film 3-4 stops results in a pretty big loss of contrast and saturation. Ektar absorbs the extra stops well and only gives you a slight color shift, deep blues turn turquoise, and the images keep their characteristic contrast.
When shot at box speed and accurately exposed the film is saturated and contrasty. I especially likes how vibrantly Ektar renders reds and greens. It's a perfect film for landscapes and nature. Ektar is a natural extension of Kodachrome, albeit with toned down saturation and vibrancy.
The one downside of Ektar is that its ISO is so low. I only shoot Ektar when the sun is out and I have a lens that can stop down to at least F4. If it's cloudy out or getting later in the day I'll have to make sacrifices that are uncomfortable with Ektar. Either using specific lenses with larger apertures or lowering my shutter speed and hoping my hands don't shake.
I haven't had a bad roll of Ektar yet even while making mistakes. The film reacts consistently to all lighting scenarios and is something I'm comfortable using in many different cameras. It's something I trust the more I use it and now something I can predict how how images will come out. That gives me a lot of pacee of mind in using it as a film for every scenario. Basically I grab it and go, it'll be fine.
You'd think that a film this consistent with such good color rendition would cost a lot but Ektar currently hovers around $5 a roll and $25 for a five pack, a bargain. With Ektar I get a characteristic look I really enjoy at a really great price point. It's a great film to start with and a great film to get stuck with in the long run.
In the end Ektar comes out on top because it behaves nicely and gives me a consistent image that I'm happy with. While there are maybe better options out there in terms of color rendition and possibly quality I don't think anything matches the value proposition of Ektar. It's the film you'll find me shooting on most days with nearly every medium format camera I own.