I own two of both. I like the New Service (I have five so far), but it does handle differently than the S&W. The Colt is a tad bigger than the S&W. Since you can physically handle the Colt, it will be easy enough for you to see if you like it or not. The factory grips suck frankly, though Pachmayr made Presentation grips for it that are fairly easy to find, and there are some others available. With the right grip, it's not bad.

Both guns are from an earlier era of high quality and are well made, sturdy guns that will last a very long time if you shoot standard .45ACP out of them. The military finish on the Colts seem a tad uglier than the S&W.

Only the first batch of Colts had the chambers bored through. After the first few hundred all Colts were chambered the same as the S&W. Most of those were refitted with stepped cylinders by Colt. Bored through cylinders on the Colt are pretty rare these days. (check "Colt's New Service Revolver" by Timothy J Mullin, Collector Grade Publications, ISBN 0-88935-498-7)

Obviously I like both, since I own both. If you can get a Colt now at a good price, I'd get it and keep looking for a S&W so you can enjoy both.