Stick with the TLR-1. It's a better light as far as durability goes.
I advise attaching the light directly to the forend. A couple of methods work for this...a short section of rail screwed onto the forend and light attached, a railed foreend (Surefire and Ergo make these http://www.ergogrips.net/item-detail.cfm?ID=4865-SHORT&storeid=1&image=moss500rail.gif) and the mack daddy solution, the Surefire forend.
Personally i think one of the first two options with a TLR-1 attached is the way to go for you.
This is the way to go, I agree. And it's what I run on my own Mossberg 590. A TLR-1 and a Mako railed fore end. The TLR-3 might be a good choice too. It's half the lumens roughly, but it's still a LOT of light, and it's roughly $30 cheaper too. I run a TLR-3 on my HK USP40 and Like it just fine. You definitely don't want all the curly-cord BS to mess with, and a stand alone light clamped far up on the barrel or mag tube does not always let you do momentary illumination. You either have it on and leave it, or off and leave it. And you can't reach it with the fore end and slide retracted/bolt open either.
I looked at the Ergo fore end, the full-length rails everywhere look like they could be uncomfortable, and can chew up your hand under recoil. And you'll have extra expense of getting a bunch of cover panels for the parts you're not using,
I like the Mako fore end for the Mossberg 500/590. It gives you the options of left, right, or center/bottom mounting for the light, and it has roughly the same size and feel as the OEM Mossberg fore end grip, save for the rail on the bottom, so I'd suggest a rubber ladder-cover for that, but it's still cheaper than covering three sides with panels.
http://www.lowpriceguns.com/product.php_372830 Mako fore-end, just a tad under $50 at several places.
http://www.cheaperthandirt.com/37979-1.html TLR-1, usually $99 most places. Sometimes on sale for $89 if you hunt hard, or find a coupon code etc.
http://www.cheaperthandirt.com/59436-1.html TLR-3, Saves you $30 bucks. More compact, half the lumens (roughly) one battery instead of two, plastic body, instead of aluminum, but still plenty bright unless it's competing with brighter lights etc.
Here it is with the Mako fore end, and TLR-1, and a Knoxx Spec-Ops, shock absorbing stock.
Close up of the TLR-1 on the Mako.
(Note, the head of the TLR-1 looks a little funky because there's a Butler Creek flip-up scope cap on there. )