Tough call as I have used both, but my vote would be for the Elite 4200 2.5x-10x-40mm. Heck, I just bought one from Jon at the optic zone last week.
The glass on the Elite 4200 is simply outstanding. In fact, I rate them as at least the same, if not a tad bit better, than the Conquest 3x-9x-40mm. In addition, the 4200 also has rainguard - which really works. In addition, the Elite 4200 is less expensive than the Conquest.
On the downside, the Conquest 3x-9x-40mm has 4" of eye relief, whereas the Elite 4200 2.5x-10x-40mm has 3.3 - but that may or may not be important to you - depending on the gun that you shoot. In addition, the Zeiss is a little bit lighter, but not by much - maybe 2 oz - if that matters to you.
I own several Elite 4200 scopes, and I love them all.
Zachary