So far, what everyone else has said as far as doing a lot of research, reading, and questioning before buying.
I enjoy reloading... on anything but a single stage.
I have 4 presses: Dillon 550, Lee Turret, RCBS Single Stage, and Lee Single Stage.
I started with the two Lee presses, set up like this:
Here's a pic of my current setup with the other two presses. (still have the two Lee presses, just not in the pic)
I used the single stage for rifle, and the turret for pistol.
I still like the turret, and still use it. It's nice for the ease of caliber change, low conversion kit cost, and low entry cost. It's also nice being able to switch easily from manual indexing to auto indexing. I currently load low quantity pistol rounds on it; IE, .44 spl/mag, .38 +p and .357 mag, .45 acp, 9mm hp.
The Dillon is far superior for loading larger quantities of single calibers. It's fairly easy to change, but requires more actions and an Allen wrench. Conversion kits are also much costlier. I load high quantity calibers on it; IE, 9mm bulk, .38spl, .223.
The single stage presses are reserved for rifle rounds, and cast bullet sizing.
If you research, and answer some basic questions honestly, you can buy something that you won't ever regret buying.
That may be a Dillon 650, or it might be a basic single stage.