DocFrankenstein said:
Is it better to know one specific film intimately, or a few of them?
IMHO it is better to know a lot about a single film than not much about a bunch of different films. Different films have different flavors, but once you really get to know a particular film, I think you'll find you can get many of those other looks and effects with the film you are using. There's nothing wrong with getting to know several films very well. Then you can decide which one is the best for you. As traditional process BW film becomes more of a specialty product we may not have many choices anyway.
I've been using Arista Pro 125 and 400 (Ilford FP4 and HP5, but "generic" so it's cheaper) for 95% of my BW. I use it for 35mm, 120, and 4x5. If I shot 8x10, I'd use it there too. I shoot about three times as much 400 as 125. I used to shoot mostly the 125, but in 16x20 prints from 4x5 I can't see the difference, and in 120 the 400 still looks really good up to 16x20 (I don't print bigger than that right now). Most of the 125 is used with 35mm gear. Most of my film is developed with a phenidone developer (basic hypoallergenic developer) such as Sprint, or lately Arista.
It's always good to try out other things though. I used to use Tmax 100 in D-76 for most of my work, and even after I switched to Ilford (mostly for price reasons), I continued to keep some Tmax 100 on hand because I liked shooting it for very long exposures at night. I still have a stash in my freezer that I thaw out a roll from once in a while. My old photo guru tells me the new Tmax 100 is not the same beast.
Recently I have developed an interest in Tri-X developed in Diafine (as my avatar caption suggests). It's definately my new choice for a high speed BW combo. I'm having great results shooting it at ISO 1250; I keep it on hand in 120 and bulk 35mm. But I only like it for low light situations.
And of course, spring is here, the clouds are huge and dramatic in the sky, the plants are growing, and there's a roll of IR defrosting on the counter right now. Everyone should try some IR in the spring! And it's just way too expensive for me to master. I shoot maybe 3 rolls a year, and often times they are different brands (although, once again, our choices are becoming limited).