Ubuntu still has distinct less/more bins. At least mine does, or the
more command is sending different arguments to less.
In any case, to see the difference, find a file that has more rows than you can see at one time in your terminal. Type
cat, then the file name. It will just dump the whole file. Type
more, then the file name. If on ubuntu, or at least my version (9.10), you'll see the first screen, then
--More--(27%), which means there's more to the file, and you've seen 27% so far. Press space to see the next page.
less allows moving line by line, back and forth, plus searching and a whole bunch of other stuff.
less. You'll probably never need
more for anything. I've used
less on huge files and it seems OK. I don't think it does crazy things like load the whole thing into memory (cough Notepad). Showing line numbers could take a while, though, with huge files.