The choice between Spintech and Flowmaster mufflers is coming down to cost. The Flowmaster setup will be the more cost effective option. A common one it is, but the Spintech setup is just mufflers, no pipes. The Flowmaster setup includes pipes.
As for which Flowmaster series, I choose the 44. It’s got that deep growl I like. The kind of growl that turns heads and keeps wannabes at bay at the light.