I use both. I tend to alternate. Squats with the BB, lunges w/ 2 DBs, leg press with BB or 2 DBs, dead lifts w/ BB. Reason - I can't do heavy squats w/ DBs - it tosses my alignment and doesn't feel right; I can do lunges w/ either, but using the DBs gives my shoulders a break after the heavy leg presses; leg press w/ BB becuase my balance seems better, and I'm fresh so I can get the heavy bar up and down all those times, dead lift w/ BB bc it is just more comfy w/ heavy wts to use a BB than a DB for a dead lift - easier on my hands.
My squat wts are 50/60/70 and my leg press are 45/55/65, while my lunges are only 40/50/60. I just have to pop on 2 1/2 lb one each end to start the squats, which come after the leg presses. If I use the bar for lunges, then I have to back wts off and recalculate; I have a 15 lb bar. Its faster just to grab DBs. And my dead lifts are 50/60/70 so I am set from the last squat. It just flows better that way.
It saves the shoulders some tiredness from not having to lift a heavy bar up and down so many times, and it save my hands from not constantly having to hold heavy DBs. I also find its easier using the barbell in increments of 10 that way I just have to stick a 5lb on each end insted of taking something off and putting something on for each wt. I suppose the same theory works in increments of 5 and just add or subtract 2 1/2 lb plates from each end each time. I also don't put the plates back in the stack after each exercise, I leave them on the floor so they are there to go right back on for the next round, saves running around. I had some timing issues w/ this one the 1st couple times thru as well, but now that I know my wts, I know the workout, and I have everything I need ready to go, its not so bad. The pause button also helps. I won't tell
Nan