I have the MGX Classic - which one next?

Listen to your heart 😉

The Helix is different enough from the MGX to be worthwhile, but if you only intend to have 2 models... you might want them to be more different.
The Progasm and Eupho would be more different to the MGX than the Helix. (Though I wouldn't describe the Eupho as aggressive)
I think the Helix Syn is overrated personally.

I love the Progasm... and honestly, part of the fun is the horror when you first open it and are shocked by how much bigger it is in person. 😮
Inserting that monstrous thing, wondering how you're ever going to manage it... ah, the fear and excitement. Totally worth the purchase price.

If I had to pick one for you, I'd say go with the Progasm Junior. It's aggressive (look at the angle of that head), but manageable and a really good all-rounder. Very different to the MGX as well.

Not to throw water on the fire, but I was not thrilled with the Progasm Jr. Not only is is larger and takes some finesse to insert, I found just retaining it for any length of time to be a challenge. Maybe my body or prostate is a little different from other Aneros guys. So judge for yourself!

It's going to be difficult for someone else to tell you what model is going to work for you. YOU are the only one that will know for sure if a particular model is going to be awesome, just OK, or does almost nothing.

It's good to have a few different models to use when one gets boring, or you just want something different, or bigger/smaller. I have "collected" several Aneros models and they all have their place in my sessions. Some get used frequently, some not so often. The option is always there for me to change things up if I desire.

I would purchase a couple more and see how you like them; they really are all different in one way or another.

Not to throw water on the fire, but I was not thrilled with the Progasm Jr. Not only is is larger and takes some finesse to insert, I found just retaining it for any length of time to be a challenge. Maybe my body or prostate is a little different from other Aneros guys. So judge for yourself!

I don't like the Progasm Jr., either.
Progasm is better than Progasm Jr., but I like MGX classic and Helix classic even more.

Helix Syn does not assert enough pressure on the perineum.
Helix has a big head and provides lots of contact area to the prostate,
but it can also numb my prostate for many days after a nice session.