I have a pair of each and have had them since they became available, the X200 was introduced about one year earlier than the Triple Cone. My opinion has not changed the Triple Cone is the better speaker of the two but I have to put a "depends" on that statement.
It depends on what your intentions are. For someone who may just be playing at home or occasionally with some friends then it doesn't matter but you can save $50 purchasing the Triple Cone. I'm using them in back line cabs so that's where my perspective is coming from.
The Triple Cone is closer to a guitar speaker than the X200 in its behavior and is especially noticeable if you are interested in EOB and vintage or cleaner tones. The X200 tweeter and crossover network are a problem for me, it's built like a hybrid of a monitor/PA speaker and a guitar speaker. The Triple Cone is a guitar speaker without the bloom at 3-4K and by pulling those frequencies down the design allows the high end to extend to 10k which is more than enough for hardware modelers.Tweeters are fine for PA speakers, stereo monitors, etc. but not for what these speakers and their intended purpose which is to replicate a guitar speaker in tone and feel.
Check out Doug Doppler on the Celestion UK YouTube channel, I think he has 6 videos comparing the 2 in various cabs with different styles. he states in everyone one I believe that the Triple Cone is a little brighter and more open than the X200 and I agree. Don't judge them by the frequency graphs which some do when they are purchasing them and don't worry about the 150 vs 200 watts. I wouldn't put an X200 in a combo and I doubt it would fit, the Triple Cone would work well.
Also, take a look at Jensen. They have 2 speakers designed for hardware modelers the N12D and the C12D. As a Jensen speaker aficionado I'm going to grab them and give then a run when I get a chance.
If your into metal and high gain, disregard my opinion, not my thing.