I've owned several McDermott's and Schon's (and still do). I'm in general agreement with most concepts expressed in these responses, summarized in the following (along with some of my opinions):
*Schon's will have better resale value in most circumstances.
*Most serious players prefer the hit/feel of a Schon over McD's.
*Schon's have a very solid hit, while McD's play "softer" in comparison.
*Older McD's, particularly D and C series cues, typically play better and carry more value than other McD's.
*Although the vast majority of Schon's play great regardless of build date, most serious players prefer the older Runde-era Schon's.
*Both have high build quality and stand behind their products (McDermott particularly shows almost fanatical warranty and product support).
One factor I consider is compatibility with aftermarket shafts. All Schon's made since the early 90's have the 5/16-14 stainless/piloted configuration with 1 silver trim ring on joint and shaft collars, making them very easy to match with any aftermarket shaft. Although some players prefer a solid traditional shaft over the laminated, low deflection aftermarket versions, I'm a big proponent of aftermarket, just for consistent playability and ease of replacement.
I slightly disagree with PDX's statements regarding custom and production cues. I think production cues can (and often do) play as well or better than full custom jobs, depending on the player's preferences. You also typically get more cue for the money with production (in terms of number and complexity of inlays/design), and they are most often easier to obtain than customs due to their lesser number of cues on the market. Custom cues have the advantage of exclusivity and higher resale value.
Good luck with your purchase. I suggest the Schon, but think you'd also be happy if you stumble across an old spliced-point D-series McDermott. I much prefer the Schon over new McDermott's. Hope this helps.