It is a difficult choice indeed, and much has to do with (as mentioned previously) the soul of the bike and the compatibility of the rider. I made this choice about 3 weeks ago, choosing the Tiger. I have long since been a beemer rider, and now very much regret the decision. One thing I really appreciate on the beemer is the attention to detail and engineering of the bike, whereas I attribute these features as the encompassing essence of the bike's soul.
I have found the Tiger to possess nothing special over Japanese models in quality and attention to detail, and in fact have found it quite poor in many areas, making it worse then Japanese bikes, and far inferior to the beemer. The wind screen / fairing combination make for the worse turbulance I have ever experienced on a bike (been riding for 10 years solid). I actually have to bring Asprin with me to work every morning because of the buffeting. The vibration of the bike overall is quite unpleasent (have had to remove and reinstall my mirrors twice since they loosen after high speed highway rides). I have seen / talked to my dealer 3 times about this, and they finally reside to "It's a characteristic of the bike." My hands still buzz 1/2 hour after parking the Tiger.
The seat has about 3/4 inch of play both, vertically and horizontally while in the highest position (in fact it popped out of the front guide while riding last week). This improves only when lowered to mid or lowest position; this I attribute to a rather cheap deisgn of placing the adjustment brackets on the seat rather than mounted on the bike as on BMWs. Even without the uneasy feeling of a seat squimring beneath you while going down the road, the seat proves far too narrow for any long-term comfort.
In all, I find the Triumph Tiger not the bike for me, since power is not my main objective (I'm a touring fanatic). As for the price, consider my recent Tiger add-ons, and determine if you may have to make the same: 1. two different windscreens for the buffeting issue ($130 /piece), 2. center stand ($220.00), 3. Heated grips ($175.00), have seat redesigned for comfort ($550.00), the two Triumph pannier bags ($1000, as opposed to $635 for the BMW equivalent). So, now I tack on about $2200 to the Tiger price over purchase, and still am not pleased, and the BMW was only 3K more. This is not including all the mods I will have to make to the Tiger in the future (i.e. to fix the vibration in the handlebars myself, since apparently Triumph designed the bike to vibrate, according to my dealer).
One last thing I implore you to do: Try to search for an aftermarket part that is specific to make and model for the Tiger. What you will find is a very small amount out there, and the ones out there are over seas. So, this means one of two things, if you can't find an aftermarket: you have to buy it from Triumph (high price, and long wait: been 3 weeks on the panniers, and expect 2 more), or wait for them to make it, which they probably won't... they've received thousands of complaints about the buffeting issue alone, with little to no windscreen mods.
I realize this response is very negative towards the Triumph, however, you can read MO's review to get to know the good things about it (except you will get the buffeting around 45-50 MPH and above rather than the 80 they listed, and the higher windscreen merely re-routes the turbulance, and shoots it around the fairing; go for the sport screen and take the wind head on). Definately ride both bikes, and get on the freeway if possible. Think about what you're really going to do on the bike, and take the Tiger for what it is: a lower-powered sportbike, that has the look and feel of an off-road. The beamer lends itself to touring moreso than the sportbike arena (80 HP vs the new Tiger's 104HP). Good luck!