I'm considering putting on a set of Meprolight or Trijicon sights on my new Bushmaster 20". Does anyone have an opinion with either one or both of these sights?  

The tritium dot is only visable from one side of the sight post. Its very possible that you have to adjust your front sight into a position where the tritium on other night sights wont be visable. Your only option at that point is to; one, readjust your front sight so you can see the tritium and mess with your zero... or two, leave it propperly zeroed and not be able to see the tritium.

The Trijicon front sight can be rotated independently of it being adjusted. Unless I am mistaken, it is the only one capable of this.

Stay with Trijicon, the mepro stuff are poor imitatios made by knock off artists over seas.
Jack

Quoted: I'm considering putting on a set of Meprolight or Trijicon sights on my new Bushmaster 20". Does anyone have an opinion with either one or both of these sights?

Both brands work well.  Both use the same material (tritium) that emits light.

The differences come in how well made they are.  Check out the warranties.

For most people either one will work well.  I have had both on pistols with heavy use - not a problem.

For rifles that are protected by the front site tower, get the one that works best for you.  Buy on price if they look the same.

mark

Front sight elements work ok, as long as its not so dark you can't ID your target.  The problem is with their rear peep sight replacement unit that has two more luminous points.  I find that these totally destroy your view of a dark obsured target because as they are so close to your eye, they both "bloom" on you.
The 3-dot systems work ok on handguns nbecause they are held at arms length, on an AR, the two rear dots are too close to your eye.
I find that using the stardard 5mm ghost ring and a single dot front works pretty good, depending on how dark it is.  
At best, you are probably only to shoot at very close range, and practice, practice, pratice will develop a good cheek weld for this type of close-in "snap shooting" using just the luminous front element.
By the way, A.O. makes a nice unit as well.
ColdBlue sends...

Also please keep in mind that a regular AR15 front sight adjustment tool will NOT work with the Trijicon front sight. The sight is too wide and will not fit into the tool. Just something to think about...
Oh BTW, I'll trade you a NIW Front Trijicon sight for one 99.9% USGI mag.

The meprolights will rotate independantly as well as the trijicons. So zeroing isnt a problem for either brand.
The front post is an A1 post with 5 adjustments. The rear has four dots instead of two so even though you cant see the dots clearly and they "ghost" out, you still have a ring of light to put the front post thru to aim. The trijicon front post is two wide.

Pt night sights has a good design. They have a verticle front post instead of a dot.