I actually bought a 11-87 last year. Great gun but honestly you will never need the 3 1/2 IMHO. I hate shooting my friends 3.5 mossberg. When we duck hunt he never uses 3.5 always 3.
Definatley get the 3 inch and not the 1100 model that only accepts 2 3/4. I remember reading that the 3.5inch model sometimes jams with light loads also. There is that new style barrel seal activator in it.
Only things I don't like is the oring gets chewed up in the gas chamber. And I hate where Remington puts the safety's on their guns. I swap barrels a lot since I have to use slugs in this part of VA. I found a guy that sells the seals on ebay real cheap though.
If you want cheap and reliable the 870 is it. Hell it's proven through time. Wally world has the best price on it I think. I know I don't take my 1187 in the duck blinds. I always drop my duck gun at least twice and it seems to stay wet and muddy throughout the hunt.
I have a Browing Citori 525 for my yearly pheasant trips, 1187 for deer and dove, and a beat to hell 870 with synthetic stock for duck.