I'm a pretty big fan of the T.H.E. pack as a day pack myself, for a number of reasons, including:
-Bomber build: 1000D cordura, double-layered in some places, #10 YKK zippers (the zippers are my main beef with London Bridge Trading bags, for instance)
-I like the design: three simple main pockets and a small internal mesh pocket
-A ton of MOLLE field, if you want to go all tactical-LEGO. Back, sides, and bottom.
-I love the use of the hi-vis yellow liners.
A couple of things to note:
1) If you're going to be carrying it separately with any real weight, I would strongly suggest adding the framesheet/stays that SpecOps sells. I found it made a significant difference in the way it carries. You can actually get a bit of weight transfer to the belt. I haven't taken mine out of the pack since I got it.
2) That said: the belt kinda sucks. Its just a 2" webbing strap with no padding. It does the job, but that's about it. I've seen some folks show where they've rigged up some extra padding on their belt, but honestly, its not the pack I'm reaching for if I'm going to carry 30+ pounds for any distance, or for more than a day hike.
3) do NOT pay full price. SpecOps has sales/coupons nearly constantly. The basic T.H.E. pack should be in the $100-$120 range on sale. The newer "UAP" version appears to be more toward the $200 range, but personally I can't say I see enough value in the "upgrades" to justify that price bump. If I ever wear out my base model, maybe I'll take another look
I don't have the ILBE assault pack to do any direct comparison, but I can say I'd take the T.H.E. over the MOLLE II assault pack any day of the week and twice on Sundays.
If you have any specific questions, let me know and I'll see if I can answer them...
-mike-