My first and favorite ritual is the LBRP. I've experienced New Aeon varients like the Nu ritual or the Star Ruby, but I really just prefer good old classic Hermeticism (I blame it on my 5th house being almost nothing but Capricorn).
I can't think of a "worst" spell or ritual I've ever done since I've been blessed to have never had a spell backfire or go awry. I credit this to the fact that I am cautious, conservative in my casting, and I divine before ritual almost to the point of compulsion. I fully expect something to go hideously wrong some day, and I hope to the heavens that I'm ready to clean up that mess when it arrives.
This is also why I won't touch goetia or enochian with a ten foot pole. Some day I'm sure I'll practice with both, but I really, really do not want one of those to be my first "whoops."
I've also had a few spells that failed and I was disappointed, but it wouldn't really be accurate to say I wished they worked. I am painfully aware of the fact that, for all my studies, I am a biased, short-sighted, mortal nitwit. If a spell doesn't work and I can't find anything wrong with the formula or my casting, I assume it was denied to me for a greater good, and probably my own good as well. I place my trust in the divine parents of the God and Goddess, and that Allah knows best - however good an idea I may have thought it was, I may very well have been terribly wrong.
The most recent example of this I can recall was a failed attempt to get into a full language class last semester. I was horribly, terribly disappointed very nearly to the point of crying. It has turned out for the better though - my illness flared up so I might not have even been able to finish the semester, and I discovered that I'm moving across state in a few months, which totally would have interrupted and screwed up my study. As different schools use different systems for teaching, transitioning part-way through learning a difficult language would have been a terrible experience and I may have ended up needing to start over in this new system anyway.
I was disappointing at the time, but I am grateful that the Divine protected me from circumstances I could not have possible foreseen.