I've owned two White's detectors, both only with stock coils, and they worked great. I've heard nothing but good comments about White's coils, so I can assume you can't go wrong with the DD1400.
I've heard both good and bad about Kellyco's Excelerator coils. Some say the quality is inconsistant. I have a little 5" Excelerator on my MXT that is absolutely marvelous in trash and is reasonably deep also. I bought a 14" Excelerator for the MXT, and it is probably best used as a doorstop. It's depth is no more than the 5" and pinpointing is non-existant, so I tend to believe (only from my own experiences) that the stories of Kellyco's undependable quality may be true. I've bought several things from Kellyco and have always found them to be nice folks, easy to deal with and fast shipping, and this is the only item from them that I can consider substandard.
Anyway, good luck on your decision. Maybe some others here can give better input on these coils.
Marc