It depends on what you’re doing and whether it’s fiction or nonfiction. There’s also a difference between a query and a proposal. And different agents might have different preferences.
A query is a letter describing the work and giving some relevant background. The goal here is to have the agent ask for a proposal.
A proposal is an outline/synopsis (they are slightly different) and sample chapters, usually three. One reason to query is to ask what the agent prefers.
I wouldn’t compare yourself to another author – at best, the agent isn’t going to care; at worst, you come off as arrogant. Let the agent read the work and make a determination.
Most agents prefer snail mail (they don’t want to print out your manuscript on their nickel to read it), but some may prefer e-mail. Ask, or see what the agent says. Ultimately, there is a lot of variation.
Assuming it’s fiction, I’d send a query, saying you’ve finished a book about X (do not summarize the plot just yet) and are looking for representation. If you have credits, put them there. Ask what the agent wants to see, and send him that.
You could include an outline/synopsis* and sample chapters are part of the process; it may even be an advantage (i.e., the agent might think, I should just tell this guy no, but, what the heck, let’s take a look at things).
Don’t send it e-mail unless the agent specifically asks for it this way.
*Outline – around 20-25 pages, describing what’s happening chapter by chapter.
Synopsis – general overview of the book, maybe about 15 pages.