My favorite club to practice with at the
driving range is the
5-iron. It is long enough that I can't get away with a bad swing.
This is not true of a 7-iron. I can swing a 7-iron badly and still hit the target. I'll know that it's not a good swing, but the feedback isn't as strong as for the 5-iron. There's just no question when you hit a 5-iron badly. The distinction between acceptable and unacceptable misses is much clearer.
The 5-iron is short enough that it's easy to swing. It won't tire you out like a driver or a 3-iron.
The 5-iron can be shaped to a large degree. It's easy to hit high, low, draw or fade.
I see far too many weekend hackers practicing nothing but driver at the range. This might appeal to the macho instinct, but the help it applies to the score you get is minimal. Practicing too many driver shots in a row is tiring. When you're tired, the quality of your practice is greatly diminished. Two quotes apply:
It's not the quantity of practice, it's the quality of practice. - Harvey Penick
Practicing a bad swing is worse than no practice at all. - Ben Hogan
Lately, I've been practicing a lot with 3-iron off the deck, varying the degree of choke down. Not only is a choked-down 3-iron a valuable asset from under trees, it also is an effective play into strong wind when a 5-iron would balloon into the next county. I've been focusing on about four choke-down positions: normal; further to the butt end of the club, with the left palm a little off the end (which I'd never play in competition, but is nice for practice); centered on the grip (my normal grip is a bit more toward the butt end); fully choked down. The variation in choke down causes a slight variation in the proper swing plane. Varying the swing plane with this single club has helped me to vary the swing plane better as I switch between clubs.