There are three basic families of film:
Most railfans shoot color slide film, as this offers the best longevity and resolution, and is also the cheapest option. A few also shoot black-and-white as well, and fewer still are exclusively monochrome. These films are also commonly accepted for publication. Most also shoot slow to medium speed (ASA/ISO 25-100) film types.
The choice of a particular slide film is something of a religious issue amongst railfans. For years, the universally accepted standard color reversal film was Kodachrome, most commonly 64 speed for action shots and 25 speed for roster photos. Unfortunately, Kodachrome has a lot of annoying qualities, including:
Kodak did, however, produce a second line of color reversal films, designed to be developed in a much simpler process (E-6), called Ektachrome. Early Ektachrome films suffered from most of the Kodachrome problems, and deteriorated in less than a decade.
Given Kodak's reluctance to improve its color slide technology, the sitiuation was ripe for a competitor-led revolt, which came from Fuji in the late 1980s. Fuji began to produce E-6 films with good resolution and longevity, and excellent color, even in lousy weather. As a result, many railfans switched to Fuji films, annoying those who believed in the old standard.
Kodak started to respond to their losses in the color reversal market in the mid 1990s, producing increasingly better 100 speed Ektachromes. Unfortunately, they have shown little if any commitment to Kodachrome, other than improving the processing equipment (K-Labs), while discontinuing the 25 speed professional product. The most recent 100 speed Ektachromes (E100S, E100SW, E100VS) are as good if not better than the equivalent Fuji products, but it's pretty clear that Kodak has lost its market dominance of a few decades ago.
About the only way to choose a color reversal film is to experiment and find a color palate you like. All of the available films render colors with subtle differences, which may or may not please you. Personally, I prefer a bit more saturation than most of the standard films provide, in order to cope with overcast skies. However, some saturated films (notably Fuji Velvia) produce cartoonish colors when used on bright, sunny days, so there is too much of a good thing.
I started out shooting 110 slide film in 1977, which was reshot by Kodak onto 24mm square Ektachrome. This option was affordable, and the slides have lasted 23 years to date. Unfortunately, I had no way of looking at the slides, and getting prints from slide film was prohibitivly expensive. So, two years later, I switched to 110 print film. I still have my prints, but the negatives are almost clear now.
In 1997, when I returned to photographing trains, I shot lots of Kodachrome 64, this being the standard bearer, as well as a reaction to the deterioration of my earlier print film. But getting the stuff processed without goofs was nearly impossible, all sorts of dandruff spots, fuzz, etc. With only one lab to choose from (Qualux in San Leandro) I just had to take what they gave me. Worse, when I'd have Qualux scan the slides for PhotoCD, they'd forget to use the K-14 process color term, and I'd wind up with purple snow. Also, most of my favorite photo locations had long-term overcast weather conditions, which washed the color out of the slides. Something had to give.
Problem was, I still liked the Kodak color palate, at least when the sun was out. So, when Kodak introduced its new saturated Ektachrome (E100VS or "Extra Color") I decided to give it a try. The results were heartening; the color was good under dark skies, and still very nice when the sun came out. I found a private lab that does good work (NewLab in San Francisco), and a scanning house (AlphaCD) that was absolutely meticulous. So, I "cut over" to Ektachrome Extra Color in May 1999, and probably will never shoot another roll of Kodachrome. In mid-2003, I purchased a Nikon Coolscan IV slide scanner, which has better depth, contrast, and gamut than PhotoCD, and it's notable that the Coolscan won't work with Kodachrome.
If you'd like to see the difference between Kodachrome and Ektachrome Extra, I'd suggest having a look at my photos from Glen Frazer. Notice how muddy some of the early shots are under cloudy skies, then scroll down to the bottom shots at Collier. Even the sky looks better.