Poll Added.

Which do you recommend?  Why?

I like the PACT III.

I have several timers and like them all, depending on what I'm doing.
CED 7000: I use it for teaching and my personal training.  The display shows the things I'm interested in (1st shot, split, shots fired and total). It has nice accessories that make it more user friendly (like the belt clip that swivels up, so I don't have to remove it to see my times).  I also have separate battery back-up for it.  It's nice and small, but the down side is that it's a little fragile, so I try to use one of my pocket pro's when running classes where it might get scratched or bumped.  I keep this one in a case in my range bag.
Pocket Pro I/II: They're pretty much the same to me.  The II has some different display settings, so it would be the only reason I might choose it over the I.  They're pretty rugged compared to my CED 7000 and I treat them that way.  They're usually in my target/gear box.  
iPhone:  I only use it for dry-fire as I don't like the idea of my phone getting "roughed" up on the range and an incoming call messes things up.

Pocket Pro 1

CED 7000 for the features and accessories and a Pocket Pro for the durability. Either are precise in timing and "listening".

I've had all sorts of battery issues with PACT III's. 

We use a stopwatch. I like it better that way so I am not conditioning myself to react to a beep.

Our methods may not suitable for everyone else, but we like how we're doing it and there have been no complaints even from the IDPA crowd that do this professionally that shoot with us on occasion.

I'm in the market for a timer myself right now. I did have the opportunity to use a few different timers at this past weekends IDPA match. The pact 2 was very easy to operate and read.