Well, now that I actually have the X, heres my take:
Sense UI is better than the UI on the X. Stock vs stock, Sense UI scrolling is smoother than on the X. The unlock screen stutters on the X. But, the Inc. uses a custom unlock screen, the X uses vanilla android 2.1. Thats one thing to keep in mind.
The external speaker may be louder on the Inc. My Droid's is louder than the X. Although games, music comes out fine.
If u wanna know how fast the 2 cpu's are, get HR Battle 3D, Google maps and start both to see. That can give u a good test. Run Quadrant and see how long it processes the first test. Load some big apps on both to get a good test
Battery life....check posts from former Inc and EVO users, maybe Droid users too. The battery life is still getting praises. There is a battery bug affecting some ppl where u have to reboot or remove the battery to see the actual battery life on the phone.
There was an OTA update recently that fixed some issues, gave ppl even better battery life, made the phone even faster, snappier. It also made things worse for some ppl....the nature of updates...lol
Size in pockets are no issue. If u have normal size pockets it will fit fine. There were times I forgot I had it in my pocket, and I was sitting a few of those times.
Size using it to one hand dial and type is no issue. And I have average size hands. I mention one handed use cuz for some reason ppl bring that up. Most of the time I use 2 hands on my lil ole orig Droid: left hand to hold phone, right hand to dial, type. lol
Only thing I see thats difficult to do one handed is swipe the notification bar down n up. I saw someone mention it being hard to use the X one handed in landscape mode...cmon ppl....lol
I try not to get into the whole Amoled vs. LCD thing, but I cant see Amoled being sharper. "Vibrant," colors that pop, yea I can see that. Sharper, I cant see it. (I quoted vibrant cuz the vibrancy is over satuation. What happens with Amoled screens is u lose detail. U lose details on Super Amoled too. Both screens have their pros and cons. Me, imma details man so I will pick LCD until Amoled gets sharper.) Screens will be a preference like the UI.
The camera....out the box, the X takes sharper close ups, the Inc sharper normal, wide shots. The X has more accurate colors. Change settings on both phones and they are both too close to really say which is better.
X has better reception. I get better reception on the X than on my Droid running Froyo's baseband, which gave me better reception than my Droid when it was running 2.1 Its kinda known the Droid had better reception than the Inc. (yea debatable but whatever...lol) Former Inc and EVO users say the X has better reception than their previous phones. The X having better reception than the Droid is very good.
Noise cancellation mics help for clearer calls.
The X has hardware advantages over the Inc, the Inc has software advantages over the X. Both phones are very similar. In the end it depends on what u want: better hardware or better software.
And like titan said, these places
www.androidforums.com or
www.androidcentral.com can give u a good idea from former Inc and EVO users. Yea former, cuz some ppl using the Inc and EVO actually switched and are happy they did.