I recently shopped Lowe's and Home Depot on the same day for the exact same item.  A tankless hot water heater. 

My first stop was at Lowe's.  I was impressed by the cleanliness of the store and the relative ease of parking. The aisles were clear and organized, more like Whole Foods than a hardware store.  I also saw a lot of bbq grills, garden furniture and appliances. I went to the plumbing department to look for tankless water heaters. I could not locate them on my own, so I asked a store associate for assistance. That initial associate did not seem to know much and forwarded me on to someone else who told me that tankless water heaters were not stocked in the store and had to be special ordered.  Glancing around the parking lot as I left I notice a lack of contractor type vehicles. Lowe's strikes me as more of a Sear's store.    
 
Next was Home Depot. The store was more crowed and appeared less organized. I headed to the plumbing department and straight to a gas tankless water heater. I questioned a knowledgeable associate and they indicated the gas one was in stock, but an electric one would need to be ordered ($999).

I needed an installer and was directed to the service desk where a long line of shoppers stood with only one associate working the desk.  Very disappointed here.  After 20 minutes I was directed to a special contractor "Hotline" phone where I was able to provide information to an operator that would then forward it to several contractors that would contact me directly for installation options.  Seems like a plan, but no calls yet.  

My thoughts are Lowe's was great for cleanliness and lawn furniture.  Home Depot is better for true hardward issues, but travel with patience.