[Lisa~]

If grip is a problem for you, then you have to decide what you want to stress the most. With moderate to high reps I'd say use the smaller bar, so you can get the reps without as many grip issues. As the reps go down (we do 6, then later 4), see if you can use the bigger bar so that your grip gets worked some too. That's just what I'd do. It makes just as much sense to say go to the thicker bar now and get your grip up to speed, but you might not get 10 reps without having to set the bar down. Either way, you're making a decision about how to work on your deadlift and your grip.