Ugh. Query Letters

Being completely new to the process of submission-- I have scoured books and the internet for the proper way to right a "stand out" query letter. And the more research I do the more dumbfounded I have become. I think that like all things, the query letter has morphed and changed over the years. Opinions abound. I have revamped my query letter three times so far during my initial agent querying process. The more I browse the internet the more I question my query letter. I know I read somewhere that leaving out the ending is a "rookie move" but the more I browse the more I've discovered you want it to read less like a synopsis and more like a book jacket. And who wants to read the end of the book on the back cover? So my query letter currently lives somewhere in the middle. I have less than twenty queries out there right now. I was hoping to get a little feedback as to which of my three queries seem more effective before I start querying more aggressively. Unfortunately the process is so slow I don't know if I can be that patient. The good news is that they have not all bounced right back as instant rejections, which as I have read, does happen. It has been a very tedious process researching agents. And because I am still so uncertain of my query letter, I prefer to query agents that require a page submission along with the letter-so that my letter, be it awful or awesome, is not the only thing deciding my success.