When you rooted your phone, you used unrevoked3. That is what you need to use to root any completely unrooted Evo. Just do the exact same thing you did before, but skip the parts that are already done (i.e. the drivers).
As for the difference between unrevoked3 and unrevoked-forever, unrevoked-forever is the method the unrevoked team devised for unlocking nand. To put it simply, it switches S-ON to S-OFF. It comes in packaged as a flashable zip, and is meant to be flashed from recovery. They also have a package that does the opposite for unrooting that will switch S-OFF to S-ON. As you learn about what root is, and how you take advantage of it, you'll realize that what I just described is a package that you flash from recovery.
So, there are three parts that make up what we refer to as full root (misnomers aside). The first part is unlocked nand (aka S-OFF). It means that you can flash any partition or firmware (like the radios) with unsigned or different signed packages. By default, the phone is locked down so that you can't write to these things with unsigned packages. You would only be able to flash what HTC allows. With this turned off, you can flash custom ROMs, updated radio firmware, etc. This is what unrevoked-forever does.
This is completely useless unless you have a custom recovery. Recovery is basically nothing more than a tiny, single-purpose driven OS. It is mainly meant for making system-wide changes to the Android system while it isn't running. Basically, you can't completely overwrite the system with a custom ROM, for example, while the system is running. This is not part of unrevoked-forever, as you need to already have a custom recovery to flash unrevoked-forever and get S-OFF. The dilemma? Recovery sits in a partition that can't normally be written to easily without S-OFF. Of course, there are ways around this, and this is where unrevoked3 comes in play, which I'll get to in a moment.
Briefly, though, the third part is a rooted ROM, and is the true meaning of the word root, in that it gives you superuser (root) level permissions in the current ROM. It means you can run things as the root user. This is needed for running certain apps such as wifi tether.
In any case, unrevoked3 goes through the process of flashing a custom recovery for you (which you can't normally do easily without already having S-OFF), flashing unrevoked-forever from the newly flashed recovery to get S-OFF, then rooting your ROM.
So, to put it simply, unrevoked3 is a process that fully roots the phone, and gives you the ability to have full control over it. Unrevoked-forever is used as a part of the process, and is provided, mainly, for:
a) Other phones that don't need to go through the whole process that the Evo does, or
b) Those who might need to go through parts of the rooting process manually, or are doing a different rooting method.
In regards to "b", there are other rooting methods out there, such as autoroot. Ultimately, they use unrevoked-forever to get S-OFF.
.
. Your in depth answers are always appreciated and my toes are in tact 