When my stepdaughter was having her baby at Bethesda Navy Hospital, I notice the Navy guards there were wearing Serpa Level 3's. I asked them on one of my trips there how they liked them. Three of them voiced their opinions, and they said they liked them because they were light, comfortable and secure, but they all preferred the Serpa Level 2 models, because they drew much faster. They said that unfortunately, they were REQUIRED to wear the Level 3 units, because of a mandate from Command.
I've never owned or used a Level 3 Serpa, so I can't speak to it personally, but I respect the opinions of these professionals who trained with them and wear them every day.
I have 2 Serpa Level 2s--one for a 1911 and one for a Glock 36, and I love them. The hood on the Level 3 seems like it would slow down the draw by a second or so once you trained with it, but it does offer an unparalleled level of retention security, if that's something you are concerned with. Unless you are an LEO, security guard, or someone who plans on wrestling or grappling with "bad guys", I think the Level 2 version is more than sufficient for everyday carry...