Which GPS System is right for me?

I have the Garmin 305 and love it. it does everything and is very customizable with the add ons for both run and bike. The new 310 is supposed to be waterproof so swim use may be possible as well. there are a lot of Garmin users on BT. Plus it sy6nc's up with the training logs so easily. I have not used the Timex so I cannot comment on that one.  

I think you will find PLENTY of endorsements around this site for the Garmin Forerunner 305.  It has some drawbacks, but overall, it is the best and most popular device for what you mentioned.  As far as interference from your partner's device, I wouldn't worry about it.  Most of the heart rate straps are coded now so there is no problem with other straps.  I have used mine with groups of other bike riders that also had Forerunner 305s and I never noticed a thing.  You can do little searching on the internet and find them for around $160 now.

X 2.

Never heard of an interference problem with the 305's, as mentioned the signals are coded.

If you don't mind going used you can probably get one for around $ 120-140 as the 310 XT is coming out and a lot of people will be selling their 305's to get that.

I just got a 305 about 4 wks ago and love it. It does everything they say and more.

I would add another 1 for the garmin 305. It will do what you're looking for and more. The only complaint people have from time-to-time is the size of the watch. You may want to see one in person before buying it.

With the 305, get the quick release kit so you can easily transfer it from your bike to your wrist from run to bike.

As far as "signals" getting mixed up, that would only apply to the heart rate data. GPS data floats through the air from orbiting satellites and GPS's like this are receive-only so they won't interfere with each other. That being said, most HR strap are now coded so they can play nicely with each other. I don't know about the Timex units specifically but you can probably check the manual to see if it's coded.

I forgot to mention I'm an extremely small woman.  That's another question about the Garmins.  Will they be too big? While the rest of me isn't exactly skinny right now, My wrist is tiny.  I"m one of those women that has to wear kids sunglasses if that gives you an idea of how small my wrist might be.

Another endorsement for the 305, but as you mentioned it is rather LARGE.  Definitely see it in person, or better yet, try it on before purchasing.  If the size is an issue, you could look at the 405 which performs similar functions but a few more bells and whistles (wireless data transfer to PC).  It is closer in appearance and size of a normal digital watch.  A large watch, but nothing like the small TV on your wrist like the 305.

One of my training buddies has one of the Garmin 305 wrist-computers.... Imagine one of those giant men's silver wristwatches with the several accessory dials set into the main watch face. Now double that, and you're getting close to the size of this thing. According to Garmin's specs, it's over 2 inches wide (elbow-wrist), 2.7 inches long (across-wrist), and nearly 3/4-inch thick....

Yes, I tried the Garmin 405 on in a store, and I'm so glad I did before buying it.  My wrists are also a bit small.  The watch face and pre-molded portion of the strap attached to the watch face were longer top to bottom than my wrist is wide.  My friend who was in the store with me was able to stick her index finger down to the second knuckle in the side of the watch while it was on my wrist. 

I also really, really want one...but they are just not reasonably sized for many women!