Back workouts - rows vs. Pulldowns
 

OPENING ARGUMENTS
Defense Rows are great for building a wide, thick back. They hit
all areas of the lats — as well as most other back muscles, such
as the middle traps, rhomboids and teres major.
... Prosecution Wide-grip pulldowns, as well as pullups, are one of
the best exercises for building wide lats due to the great stretch
they place on them and the downward motion of the arms.

EVIDENCE
One study found that when trained lifters did wide-grip overhand pulldowns, they used more muscle fibers in the lats than when they used an underhand grip or a neutral grip on a V-bar.

A study from the Canadian Memorial Chiropractic College (Toronto) directly compared lat muscle activity on wide-grip pulldowns to that on rows. When subjects did seated cable rows, muscle activity of the lats was more than 40% greater than when they did wide-grip pulldowns.

VERDICT: ROWS
Rows appear to be a better exercise for stimulating more of the lat muscle fibers and, therefore, helping to build a bigger back.

SENTENCING
Starting most of your back workouts with rows will help you place more overload on the lats (resulting in increased muscle size). Although the Canadian study used the seated cable row, we suggest that you use the barbell or dumbbell row at the beginning of your workouts when you are strongest and include other versions of rows later in the workout. You should also do a variety of pulldowns and/or pullups and, occasionally, start your back workouts with pulldowns or pullups. If you can’t do more than 10 pullups, do them first in the workout (before you’re fatigued), so that you’ll be able to complete an adequate number of reps for stimulating muscle growth.

I prefer rows over pull downs. Either barbell or dumbbell over machine. Of course, from time to time a good pull up with a 45lbs plate hanging from your waist do the trick. Probably is a good combination if we do both in a routine session.