I've had both...started out with the slash cut basics and then later to ovals. Like the looks of the ovals better...but switched back to basics because I liked the sound better. I guess I had the basics for so long, switching to the ovals just didn't sound right to me. Either way...you won't go wrong. JMO.
I have the basic slip ons and the sound is just perfect for me . They do get a little bit louder as they get older , but I think all pipes do.
The ovals are nice but they sounded a bit "tinny" I>M>O> .
I have 2,800 miles on the Ovals and really like the look. After I had them on for about a thousand miles though I didn't feel that the sound was deep enough so I drilled (3) 1/2" holes in each baffle plate, nice deep sound now. I don't think you can go wrong with either one of your choices since Vance and Hines makes a good quality product. One thing about the Ovals that sold me was the fact that the stainless steel inner pipe has no contact with the outer chrome so the bling will stay nice for as long as you keep it nice.