I have mixed feelings about portrait vs. landscape formats. They both have their pros and cons. As for space at the table, I usually put my character sheets in a notebook with plastic sheet protectors. I look up things on a character more often than I update anything, and I print out a new sheet every few sessions (I make my characters on an excel spreadsheet, or in the case of GURPS, a program just for that game system).
What it really comes down to is layout. There are things that fit better on a character sheet in landscape than they do in portrait. I used landscape to very good effect when I played in a
3e version of the Dark Sun world. It also worked quite well for the d20 Star Wars game that I played in. Alternately, before I had the GURPS character program, I used a spreadsheet for that and I preferred the portrait format.
I would suggest that you play with both and think of why you prefer one over the other. Or better yet, if you go to the effort to try both, why not offer both?