I've had both tandem and triple axle toy haulers and along with that experience it's given me some opinions. Those opinions are probably not going to agree with the views of some but they are "my" observations and opinions, here goes....
A typical "tandem" axle toy hauler will come equipped with roughly 7k axles and 16" wheels using E rated tires. The triple axle units typically use 5k-6k axles 15" wheels and D rated tires. Let's say you're looking at a triple that uses 5k axles, that's 15k rating on the axles whereas a tandem using 7k axles gives you 14k. It sounds like you've gained another 1k but in reality that 500 pound axle/wheels/tires (at least) has diminished the advantage by at least half.
Here's the opinion part: I believe that since the demographic of the purchaser of these toy haulers is overwhelmingly male and for us more is better then the additional axle is largely a marketing gimick, one that we as egotistical males are often willing to pay extra for.
Now here's the part that's not opinion but real world practice regarding the triples: Our latest rig is a triple axle and as such does in fact have some advantages, whether they are worth the extra money I'm not so sure, but they do have some advantages, one of which happens to be ride quality. The tandem axle units tend to give a rougher ride in the stern, which unfortunately is where those of us who use these things just happen to put our big heavy toy(s). The smoother ride of the triple axle is actually kind of nice, especially on the days that you forget and leave your cordless drill sitting on one of the counters back there and it doesn't go bouncing around and end up in pieces all over the garage. I have as an experiment also left a pop can half full of water on the work bench right next to my ramp door and driven over 400 miles to find it just where I left it. On the other hand I left the trunk unlatched on my Electra-Glide more than once in our tandem and found everything scattered including the asprin which had found a way past the child proof cap. The triple axles also tend to be "slightly" more stable in cross wind conditions.
The real advantage of the triple is the brakes, you've got two more. This is something I've been aware of for some time in that for years I pulled tankers and I always appreciated the times that I had triple axle lead and pup trailers, they stop better although there are more of them to adjust.
I'm sure that there are tandems out there that ride just as well as the triples and even come equipped with disk brakes. The big thing that you really need to investigate isn't so much how many axles you have but the floor plan (it sounds like you already have) and most especially the "payload". I've seen a lot of toy haulers that look really neat but when you look at the numbers they just don't have the payload capability. I've actually run across more than a few that had a payload of only around 2,000 pounds, that's not much when you consider that a toy hauler will have a pretty large fresh tank (100-150 gallons), dual grey tanks and you're going to stick a VERY heavy object in the rear. The 14.5k GVWR on a 39 footer sounds kind of light to me (I read the specs as 15.5 on their data sheet), ours is 40 feet and we hit gross at 17,500 pounds with just the bike, water and provisions. If we load the Rhino we're actually over by about 500 pounds. The one thing that concerns me about the Torque is that it's a triple slide with a low GVWR and it makes me wonder what the payload (usable cargo load) actually is, I don't see it posted on their data sheet. Find the spec sheet located inside one of the cupboards and find out what the empty weight actually is (they are required to individually weigh them after manufacture) then subtract that from the GVWR, I'd be curious to know what numbers you come up with and they may be more than adequate, but you really want to know before you plunk down money.
Don't sweat the number of axles as a primary issue, I cringe when I think about what it costs me to replace the tires on my triple but it happens to be what we got and it works for us. I wouldn't hesitate to buy a tandem again although they are getting a little rare in the configuration that we like, although that Torque is VERY nice.