If I ever get time I'd like to replay MP1 and 2 on Wii. I used to prefer Echoes to Prime because I actually got stuck in the final part of the first one, possibly the final boss. I ended up beating Echoes before it, and then decided to restart Prime. The Light Suit is probably my fave suit in the series. But I think now I would say MP1 is the better game simply because it was the first one since Super, and really delivered on so many levels.
Metroid II was the second Metroid I owned, and really enjoyed it as a kid. Other M I enjoyed overall. I liked the style of it, but it was too linear and easy. The final part of the story really bigged shit up, only to not deliver at all. I definitely wouldn't say no to another Metroid game in that style though.
I think Nintendo will play it safe and do a side scrolling Metroid next, on 3DS. Maybe try to persuade Retro to do another FPS one on Wii U too, because they know they sell over here. But it's still a bit misty as to what we'll see next.