I don't have an XS to compare the meter to, but I recently got a CoaguChek S, primarily out of curiosity about why one was preferred over the other.
The ProTime 3 is quite a bit larger than the CoaguChek S - and I think the XS is even smaller. If size, or portability, are issues, the XS or InRatio may be a better choice.
As far as accuracy - my two meters don't always give the same readings. Because the ProTime cuvettes have two quality controls built into their cuvettes, I've been pretty confident in their readings -- last December, after I had a concussion, the hospital lab's reading (2.92) was almost identical to my ProTime 3's reading (2.9) the previous day. The CoaguChek XS and InRatio strips also do quality control.
Marsha's correct about the battery issue. The ProTime 3 has internal batteries. The XS uses standard alkaline batteries or an external power supply, if I recall correctly. The batteries for the ProTime 3 aren't that difficult to replace - but if you go with the battery pack available from the manufacturer, they can cost quite a bit.
Additionally, the ProTime requires quite a bit more blood than the XS and this may be an issue for some people. (For myself, I've wasted more strips for the CoaguChek S than I have for the ProTime because it's not always easy to get that one, large drop onto the little spot on the CoaguChek strip. The CoaguChek XS makes it easier to get blood into the strip - touching the side of the strip will start the capillary action that brings the blood into the strip).
The ProTime 3 also takes longer to give you a result. (It may be the only meter whose action actually waits for the blood to start coagulating, rather than using other technologies to get a reading). In my experience, it could be anywhere from 2 to 5 minutes - plus a minute or less for the strip to warm up and the time it takes to incise the finger, transfer it to the lancing device and then to the strip.
Personally, for me the learning curve for the ProTime and the ProTime 3 has been pretty short. The issue with refrigeration required for the strips is a bit of a hassle - but it's because the thrombin used requires refrigeration.
Strips for the ProTime have cost me about $5 or so each - and I waste very few. The CoaguChek XS supplies probably cost about the same as the ProTime cuvettes - and ProTime includes a lancing device with each cuvette.
One other thing - I was able to buy my ProTime and ProTime 3 meters on eBay. If you're not insured, or pricing is an issue, this may be something to consider. (I've bought ProTime meters for $50 or less, and a CoaguChek S brand new for $40. The meters have worked for me). Personally I wouldn't buy a CoaguChek S - even if you get a good price - because Roche said it won't support the meters after October 2011. This may not be entirely accurate - I've seen some strips for the CoaguChek S with expiration dates in 2012 being offered.
And one final comment -- the ProTime 3 has a loud beep (which can be turned off in the setup menu). This beep upsets my dog, so I usually close the door to the room where my dog is, and go to another end of the house to do my testing.
I hope this information helps. (I like my ProTime 3, but may be getting an InRatio in a week or two, so I can evaluate THIS meter, too).
I'm unaware of the ability to transfer your results to a computer. For myself, I keep a spreadsheet with my INR data and just update it whenever I test. The ProTime 3 will store 30 tests.
