Over/under, in theory, is easier on your grip and therefore allows you to hold heavier weight. I personally think the over/under grip is awkward and uncomfortable, so I never do it. I always do over/over for deadlifts, and I do under/under for bent-over rows.
I like over/under bc it's how I learned to do deadlift back in HS and it just feels more natural and my balance is better.
I'm transitioning into a routine w/ more cardio. This week was hell cuz I hadn't done much cardio in awhile so it's one of those things where you forget how to push through the pain. Today was good tho... I did arms only (when I was focusing on lifts I was doing like, 3 muscles a day), then I did about 3.5 miles of interval running, changing it up every 2-5 minutes, and then I was going to go home but it was absolutely beautiful out which is really unusual here, so when I got home I changed into fresh clothes and jogged up the street about a mile to this KFC where there's a tree with a perfect pullup branch and did about 45 or 50 pullups in sets of 10 and then jogged back home, great day.