Have you seen the photos of the two different Compacts on the Home page here? There are also photos of the Hunter I, which looks similar to the Compact II.
Looks-wise on the outside, the Compact Jr. is more of a shoebox shape, and a bit simpler. The pop-up roof is full length. The Compact II is a bit more stylized, with some slope to the front and some ridges and the like on the sides. Inside, it is a bit larger, with an extra foot or so on the inside. The pop-top is smaller and is only over the rear section (kitchen etc) and not over the bed. They both typically have slider windows
, and a regular RV type door on the rear. The Compact Jr. windows
are typically square-cornered, whereas the Compact II (I believe) usually has radius-cornered windows
On the inside, the Compact Jr. has two fore-and-aft beds up front, which can either have a table in between or be made into one huge bed of about 72" wide and I think about 77" or so long (although don't quote me on the length). For that you would sleep lengthwise. Some people (if their height allows) sleep crosswise on the forward most section, and then have a little "dinette" on the after section.
Behind that, at the rear of the trailer, there is a kitchen on the left (driver's side), and a closet area on the right. There are walls between those areas and the bed area for support.
The Compact II is laid out similarly, although I think the bed is a bit wider and perhaps a bit shorter (fore-and-aft). I guess because it is wider they expect you will sleep side-to-side in the trailer, and thus it does not need to be as long (fore-and-aft) as the Compact Jr.'s bed.
At the rear, the space is similar. With the extra space I think it can vary, but there is often a bit more closet between the bed and kitchen/back area. Sometimes a Porta Potti "room" or even a plumbed bathroom. I've seen some with ovens (as a part of the stove).
It seems to me that the Compact Jr. more "came one way," and the Compact II's had more options and variations in level of accessorization.
The Compact Jr. has a "stick built" interior for the most part, and I think the Compact II does too. The kitchen "hood" may be fiberglass, but most of the interior furniture is wood.
Compact Jr's sometimes have bare (painted) fiberglass walls on the inside and sometimes have a vinyl-covered, diamond-quilted, open-celled foam wall covering (but from what I have seen it is not bonded to the walls in the same way that Ensolite usually is). I'm not sure if the Compact II's all have the vinyl or if some of those came bare too.
The Compact Jr's were made in two "side halves," whereas I think the Compact II's were made in top and bottom halves.
The Compact Jr's have a leaf spring suspension; not sure about the Compact II.