Revo Sweep

This can easily be answered by just looking at the DMX traits table in the manual. The 3 channel mode gives you control of color and select a chase and also strobe the fixture or change the speed of the chase.
28 channel mode allows you too control each individual LED. so you can make and playback your own custom programs or scenes using a DMX controller. However depends on your controller you will have to make sure your controller has blocks of channels of 28 or more. Unless you are using a software DMX program like MY DMX or Compu Live. hope this makes sense.
Sincerely,

One of the nice things about such fixtures is the ability to change your mind later on.

What I'd do is if I wasn't sure, I'd mess around with 1 in 3 channel mode and 1 in 28 channel mode, either at gigs or on your own time. See what you like. Then try both one way and both the other, and again, see what you like.

I do strongly back Jingle's suggestion about going with a software controlled platform unless you have the funds to go for a rather full featured lighting desk.

There really is no best way to answer your question. Screw around with them and figure it out. In my similar situation, I hvae 4 Mega Panels. I've chosen to go wiht 7-channel mode, it works best for me. In fact, currently, all my LED fixtures are in 7 channel mode. The consistency and how I use them, this is a ideal match. The Mega Pane I think has a 26 channel mode, but for me, especially with how the default profile is(but mainly how it works), it's just not something I will utilize, at least not for a while.

Thanx for the quick reply guys, I am using MyDMX to run everything. Which, by the way, I have another question about what seems to be a stability issue which I'll post on the MyDMX forum...