Like most people here Laura, I would always put a technically sound demonstration of an easier pattern ahead of a porrly performed difficult pattern. Basics are basics, and if your basics are poor then you simply cannot achieve a high mark. I would liken it to how judges score gymnastics routines:
The top mark you can recieve in gymnastic competition is a 10 from a judge. However, your personal top possible mark will be different according to how difficult your routine is. So a reasonably easy routine may only be given a maximum mark of 8.5, in which case if the routine is performed perfectly you can get no higher than an 8.5 for it. However if the routine is very difficult it may be given a top possible mark of 9.8, but only if the routine is performed perfectly. Large mistakes will be very damaging to a score as will sloppy technique.
So, in conclusion, harder patterns should have the potential to be scored more highly, but sloppy technique should always be punished in judging a pattern, and the easy pattern performed well should usually beat the hard pattern performed badly.