Which on would you prefer? What are the pros and cons of each system?

I know we have discussed this before but here is my take on it:

I trained with ALICE gear for 17 years, and still prefer it over any vest/molle/etc. systems.
I do however use an improved H-harness in my setup.

Pros: cheap
         available
         proven (and improved upon by various makers)
         
Cons:
          not versatile (according to the gear snobs,I say BS)
          uncomfortable (learn how to setup your sh*t right)
          the GI Y-harness sucks (H-harness works 1000% better)
         

Like it or not MOLLE is here to stay.  Most dedicated pouches these days are MOLLE although some can be used with an ALICE type set up.  Personally I just converted everything to MOLLE and so far I can find nothing wrong with it short of the initial set up...weaving those MALICE clips can be a PITA.

IMHO the MOLLE vests and carriers are much more comfortable.  Your load does not have to be perfectly balanced to be comfortable.  I used my ALICE belt and suspenders for a long time and the thing I hated most was once my canteen got 1/2 empty or I used up 1/2 my ammo everything started shifting and bouncing in different directions.

Good Luck

Alice was good in its time, but MOLLE offers many options that aren't possible with ALICE.
Another thing, since most manufacturers consider ALICE to be somewhat obsolete, you will have a hard time finding quality, updated items.  For example, I have old ALICE pistol mag pouches.  These are GI with a snap.  Newer MOLLE items come in a variety of better closures and materials.

Alice is all we're allowed to use while stateside, with a bit of relaxation on uniformity when we deployed ISO Iraqi Freedom II

There are SERIOUS shortcommings inherent to the issued gear if you are not Pvt Joe Snuffy rifleman.

Even as a regular troop issued an M-16 (or varient), there are drawbacks to being restricted to using the issued LBV.

If you arent completely average (height, weight etc) you will have some problems with the gear as issued.

I'm 6'5" tall, and a bit on the husky side, my LBV doesnt fit right no matter HOW you adjust it. AND... if that isnt enough, I'm a saw gunner.  What do I need with four mag pouches that regularly sit empty?

I have a Spec-Ops brand H-Harness and SAW pouches attached to my pistol belt.  I replaced the back straps with a hydration carrier, and attached a buttpack.
It carries everything I need, (though I want a drop leg for 30rnd mags), and doesnt shift all over the place when I move, without constricting me at every turn.

Ultimately, I guess it comes down to personal preference...  Only thing about ALICE that seriously needed changing was the attachment system, MALICE clips fit the bill perfectly.

I concur with the above comment about the Y harness. Not long before I left the Army, in 97, I wisened up and started using an old Vietnam era H-harness I picked up from a surplus store. It was so comfortable and worked well with a ruck. Like Pointman said, setting up an Alice LBE so it works well for the user takes time and effort, and some painful trial and error.

What can you really do with ALICE?  You can put the pouches on your belt and that's about it.  You can attach some very small (like first aid pouch size) pouches to the shoulder straps and then what?  If you are using the suspenders, you have tons of wasted space on the chest, and still have the problem of not being able to use the waist strap on a ruck/backpack for carrying heavier loads (bad for the back).  If using the LBV/ELBV you have the chest pouches for mags, and can add some more on the belt, but you are stuck where the chest pouches are, and again you can't use a waist belt.