A lot of people talk a lot of advice on demo reels. Some good advice others not. I'm going to break it down really easy for you all. Every company in every industry has it, it's called the bottom line.
A company gets paid to DELIVER FINAL SHOTS. Thats what they do, thats how they make their money. They hire artist to do the work. They look for artist who can do as much of the work as possible, meaning do the most work with the least # of people (less overhead costs). Even if he/she is expensive if they can do more/faster work, better for the company. In other words, companies hire artists who they believe can FINAL SHOTS. Jr level demo reels are for artist who want to show they can final shots. If a reel doesn't show that, they don't get hired. A Jr guy who's 1/4-1/2 the price of a Sr guy needs to show they final 1/4-1/2 the number of shots a Sr guy can, simple as that. If your reel doesn't have one final looking shot, how can a company bet on you that you'll be able to final a shot later? Thats usually why Jr guys don't get hired. At LEAST ONE GOOD SHOT is a must. Forget about what software, think about what techniques you can do or show. Get one great shot. Finish that and still not have a job? Do another.
Some nice examples site (and yes most of them as 3dmax/fume guys) I have and am learning from their site design and am inspired by their fx shots. You don't need to do all this but get damn close if you can. Look at these for their tests and their shots. Don't worry about their tools. Think about what you know and what you can do, how can you show that? Bottom line :D
Lot of props to these guys for taking the time to get their work, show some of their process and getting it up online... that's a big pain in the ass, as most FX guys I know don't take the time to do that, me included.