What would be the best Linux Distro to use with a Dell Optiplex?

I’d say it all depends on your experience with Linux. If you’re more experienced, go with something like Crunchbang. If you’re not, try xubuntu. That would be fast on an older machine.

ubuntu. most compatible.

Are you new to Linux? If so, Ubuntu is probably your best bet. It is very user friendly, and has a huge support base.

As @reactor5 above me has said, xububtu is a good distro for an old pc. It is a variant of ubuntu.

If you’re really going for speed, consider Damn Small Linux (DSL) or Puppy Linux as well.

@eambos Crunchbang is too, actually. There are a ton of derivatives, eh?

I would just try ubuntu first. You can just burn the ISO and run it from the cd to make sure everything works. If it does then you can install it.

This computer is plenty powerful for regular Ubuntu, those light distros would be suitable for something more like a Pentium II with 256MB of RAM and integrated graphics.

You could also look into Fedora, it’s a nice polished distro as well.

The best distros I’ve used are Ubuntu and Linux Mint.

Debian comes with over 25113 packages, precompiled software bundled up in a nice format for easy installation on your machine; Ubuntu is Debian Based.

Ubuntu (and its derivatives: Kubuntu, Mint, etc) are distros with the highest levels of hardware compatibility. If you want all of your hardware to “just work,” that’s what I would recommend. Other than that, it’s really up to personal choice.