2004 Litespeed Siena, 1996 Litespeed Obed, 1992 Miele (unknown model), 1982 Meile Uno LS.
The shadow is the low profile design with a more direct housing routing. If you need a barrel adjuster at the derailleur end, you'll need to get an older model. I have 3 generations of XT derailleurs installed at the moment, all are working flawlessly
It'll help to list what type of bike you've got, what type of riding you plan to do with it, and the gear sizes of your rear cassette. The longer the cage, the bigger the range of gear sizes it can handle (since the gears with fewer teeth take up less of the chain, the derailleur takes up the extra chain length so that the chain doesn't go slack).
Assuming you have a mountain bike (sounds like it from the 3x7 gearing), SGS has been the standard for most mountain bikes for some years now, so I'd go with that. If you ever go for a "Megarange" cassette with a large range like 11t to 34t in the rear, you'll need it, and there's not really a practical drawback. (the arm on the derailleur, being longer, will hang down lower, slightly increasing the chances of it hitting a rock or log or something in really rough terrain)
Given that your current bike is 3x7, it sounds like it's a lower-end bike. Personally, I'd probably go with a Deore RD at 1/4 to 1/3rd the price of an XT RD for such a setup. You can always upgrade to an XT later if the Deore fails on you. Here's a Deore for $22: http://www.cambriabike.com/shopexd.a...%20DEORE%20RD&
Thanks for the clarification - have fun with the upgrade! You might also think about upgrading to 8 speed in the rear while you're at it -- 11t to 3Xt is less jerky with 8 steps than 7, and 8spd cassettes are quite cheap these days.