Honestly, everything varies by store, not chain. I worked at both HD and Lowe's in HS and college (at home during the summer). HD was infinitely better in terms of employees. I think a big part of it comes down to the fact that each store has its own HR person that does hiring for the store. If they're bad, everything suffers.
Both chains track how much you spend by CC number and card name. They also know how much the average person spends there and focus on customer retention because a lost sale is lost future sales. Corporate doesn't care if it takes giving you 10% off a ceiling fan to keep you from going across the street because they want you coming back and spending $50k there over your lifetime. ETA This is really pushed by both during training. Both companies have a policy of beating the other by 10% if you find something cheaper at the other. They also have policies, or did, of price matching similar items like light fixtures. Hunting Bay is HD's brand, so you won't find it at Lowe's or anywhere else. But if you're going to buy a similar looking fan from Lowe's because it's $20 cheaper, there's a good chance HD will price match to keep you happy and shopping there. Same goes for Lowe's. It's the employees and managers who generally don't want to engage in customer service because it's harder and hits the local (store) bottom line. Plus, not many people are going to try to cut through red tape for some rando and $15/hr.
Storytime...
While working at Lowe's, I had an elderly lady come in looking for help with a door she'd bought through Lowe's. I think it was something like built in blinds. My lazy department manager brushed her off and said she'd need an entirely new door for like $350. I thought that was bull**** and offered to check if we could special order something for her. He straight up told me not to waste my time in front of her and walked off. I spent like 20 minutes looking up her door info in the catalogues we kept and potential solutions in our special order system. We didn't have anything that could help her, but instead of giving up and trying to sell her a door, I called the manufacturer directly and talked to a rep to see if we could special order something directly through them instead of the system. Turns out, they couldn't sell the parts she needed to us, but they COULD sell directly to the customer for like $50. This lady was ecstatic because she couldn't replace an entire door herself and wouldn't have to spend another $300 to replace a perfectly good door. I got everything started for her through the rep so all she had to do was call a number and give them some payment information once she got home. No need to know part numbers or anything because the order was already ready, and they'd ship directly to her house instead of her having to come in and pick it up (it was a rural community and she lived outside of town). Department manager was PISSED because I "wasted" so much time on her, but he couldn't do anything about it because no one in actual management was going to get mad about going the extra mile and making the customer happy. That guy was still there 10 years later when I dropped by to pick up some stuff for my mom's house.
That said, the employees at the Lowe's near my house are infinitely more helpful than the employees at the HD, who are completely useless. They tend to be better stocked as well. I used to go to HD for everything, but now I go to Lowe's first. It all depends on the store.