What film speed do you like your prints best at? That's the speed you should be shooting at.
Making negatives that work well with the rest of your work flow will remove a ton of frustration in the darkroom come printing time. And to make such negatives, some testing is required.
You are probably unique in what your situation is, and if you think about it, all of these factors play into what speed you should expose HP5 at to give YOU pleasing results:
- Your lighting conditions / quality of light where you live and photograph
- Your metering technique
- Your meter accuracy
- Your lens
- Your shutter accuracy
- Your water supply
- Your film developer
- Darkroom thermometer precision and accuracy
- Your film developer dilution
- Your agitation technique
- Your printing paper
- Your paper developer
- How long you develop your paper for
- Paper developer dilution
- Darkroom 'safety level' (how dark is it really, and is your safelight safe?)
- Are you going to tone your prints or not?
There are a zillion factors that play into how you should expose your film!
Now go shoot some film, have fun, and figure out what you must do to get the results you want.