All the current DirecTVs are identical on the inside. The only model differences are drive size and case (the look of the box).
The traditional grid guide is slow on all of the DirecTV Tivos. The Tivo-style guide is much faster, and generally preferred for that reason. Press the ENT button on the remote to switch to the Tivo-style guide.
Once you've had a Tivo for awhile, you probably won't use the guide much, because you'll watch all your favorite programs on your schedule (recorded, not live), without commercials. Features like search by title and wishlists eliminate the need to use the guide to find your favorite programs.