I recently returned from a business trip to Vegas and spent 5 nights at the Signature. We happen to be a fan of staying in the MGM as its right on the monorail path to the convention center, and dealing with that cab line on the way out of the LVCC is never fun.
As for the rooms, they are absolutely great. Spacious rooms and big bathrooms include the Jacuzzi tub. Everything is well appointed in the rooms.
As for that walk to the MGM...I am very much proposing the MGM start an annual out and back 10K down that hallway. I happen to be that guy who enjoys walking everywhere over a short taxi ride, even in the Vegas summer heat, but walking that hallway out to Tower 3, 2-3 round trips a day, really got to me with 6 days of it. If I was only around for the weekend, I likely would not have much to moan about.
If you decide this is the place for you, I recommend checking out: http://preferredhotelgroup.com/preferred/destinations/united-states/nevada/las-vegas/the-signature-at-mgm-grand
The Preferred Hotel Group has a stake in a number of the rooms here and often seriously undercuts the MGM rates. On my stay, through Preferred Hotel Group, I got a Breakfast Package that included room service breakfast for 2 each morning, for less than the room only rates for the MGM or The Signature. The website rates also dropped as I got closer to the travel dates.
If I came to town for fun for me, I'd likely go Cosmopolitan, Wynn, or Venetian.
Next time I'm around on business, I'll likely go back to the MGM as the redone rooms there are greatly improved over a couple years ago. If PHG offered a smoking rate with room service breakfast next time I'm back on business, I would definitely be tempted to book Signature again, but likely have a 'what was I thinking moment' every time I walked that hallway.