You can't go far wrong with Ilford HP5 IMO. I use it almost exclusively in 35mm and extensively in 120 format, it's incredibly forgiving and produces sharp results with little grain. I use Ilfotec HC developer so I'm not sure how it would react with other solutions.
Tom Bertilsson made a good point: Find a film and developer combination available from a company that is going to be making it for a while.
I wish it was that easy. I thought I had done it. Eastman-Kodak Company's Panatomic-X in their Microdol-X. Then they dropped Panatomic-X, so I went to another high resolution film. Five years ago, they dropped that one. About a year later, they even stopped making Microdol-X. I do not want to go into the subject of papers for printing. At times it can be a challenge to be a loyal customer.
Now I am still experimenting with other films from different companies and developers from Photographer's Formulary, Freestyle, Eastman-Kodak, and maybe a few others. I am not able yet to say that I am really learning anything about all of these films and chemicals. At times it is not easy to remember which one did what, and what I could use that charactersitic for, if I could remember which one did it.
Ralph Javins, Latte Land, Washington
When they ask you; "How many Mega Pixels you got in your camera?"
just tell them; "I use activated silver bromide crystals tor my image storage media."
Kodak's been making tri-x and tmax 100/400 for a long time. Since tmax is the newest product and quite versatile, I wouldn't be suprised to see tri-x discontinued sort of like their color consolidation "Use this instead; it's better and more versatile". I bet they still sell a lot of tri-x and wouldn't do that anytime soon; it would be a bigger deal than kodachrome. Tmax100 effectively replaced tech pan for grainless copy work, so there was no need for tech pan and it was discontinued despite it differences. I use kodak because I like the product quality, and I like the results I get from 20 years of experience in using tmax400 and I can use it in all the formats I shoot; other people have got tri-x absolutely nailed in achieving the results they want. That's the benefit of sticking with one or two films and no more. Other people work best with ilford, fuji, foma, etc and they make some good stuff too.
Paper is a much shorter feedback loop and I've adapted to different papers much more easily. Where film take a long time to shoot, transport, process, analyze, paper goes from being exposed to minutes later being washed. As soon as it's dry (perhaps an hour or less for RC stuff), you can see what it does. Compared to film, it's a simpler product with a narrower range of usage. I figure a handful of prints and I'm up to speed dealing with a new paper. Try out different contrasts, drydown, development times, etc...