It totally depends. I'm a girth wimp, so I got the JR. If you like girth, the larger one would be better. The larger one also will be a bit better for firmer g-spot stimulation, and the larger one has more texture.
I have to agree with Ryuson; it just all depends on what you're looking for.
The original has more girth and is a little firmer. It's more filling and better for g-spot/p-spot. Plus, the details are better on it. I don't find the suckers as realistic on Jr. The suckers are more subdued, and the surface is very smooth. It's also more wiggly.
Generally, I prefer the original for vaginal penetration, and Jr. for anal. Of course, Jr. doesn't have that great of a base for anal. So, be careful with that. Of the two, I'd say the original is less likely to get sucked up your butt. It doesn't really have that great of a flare to the base either, but it's better than Jr.
Depends on what you want. The tentacle is very, very girthy and it has an extremely pronounced texture. It's not for the faint of orifice. Tentacle Sr. also has quite a dramatic curve, which hits all my spots really well. I personally love it, and I wouldn't have been as excited about the Jr., but if you know you're not gonna like the 4" wide base and rough suction cups, go Jr. It's still adorable, and it still glows in the dark. And I'm pretty sure it's cheaper.
I like the Tentacle, Jr., best. The Tentacle is good, too, if a bit large. I love the texture on the Tentacle, but I'm not crazy about the placement of the texture. I'd rather the texture be on the inside of the curve so it can pass over my G-spot. Instead, it's on the side, so it rubs my side-wall.