It depends on what sort of slide/bottleneck sound you are trying to get. Kelly Joe Phelps uses a Gibson flat-top played lap style and he gets a fabulous clean sound, but this is in large part because he is a virtuoso player of incredible accuracy. Fred McDowell used a shitty old archtop held together with tape for his first recordings and bottleneck blues playing really dosn't really get any better than his stuff. He used bottlenecks he made himself from real glass bottles. Old blues guys like Blind Willie Johnson tended to use inexpensive guitars - they hadn't the money for good ones and you didn't want a quality instrument for busking in the street - and got a great sound. The Tampa Reds and the Memphis Minnies of the world bought the most expensive guitars of their time, National Resonators, because they were rich show-bizzy performers and were concerned with image as well as sound quality and volume. Significantly they moved on to electrics when they came on the market. My feeling is that in general contemporary acoustic guitars are ill-suited to bottleneck playing, their construction is too light for the heavy gauge strings you need for a good sound and high action. Many modern guitars are built for wimps who like a tinkly-tinkly finger picking sound - I don't want to mention names but, hey Leo Kottke. Your Blind Boy Fullers used resonator guitars, high action, heavy strings and metal thumb and finger picks. If you want that sound, thats what you have to have.