Sorry people, need some help on deciding Pokemon! I need to decide between..

Question for Pokemon Emerald

Sorry people, need some help on deciding Pokemon!
I need to decide between Cloyster, Lapras, Milotic, Blastoise and Kingdra, and maybe that'll help me come to a decision.

And also, I think I've FINALLY worked out what Altering cave is!

Well first of all, you need an E-Reader. And then you need 8 Altering Cave E-Reader cards. When you scan card #1, the zubats in the cave will be replaced by Mareep levelled 5 to 13. When you scan card #2, you can catch Pineco at levels 19 to 29. And I can't be bothered doing it anymore in this format so I'll switch to this one:
#3: Houndour (lvl 12 - 22)
#4: Teddiursa (lvl 18 - 28)
#5: Aipom (lvl 18 - 28)
#6: Shuckle (lvl 18 - 28)
#7: Stantler (lvl 18 - 28)
#8: Smeargle (lvl 18 - 28)
Well, there you go. All the Pokemon you can catch are pretty bad, maybe Teddiursa and Houndour are alright, but you can catch Teddiursa from somewhere I don't know and you can get a Houndoom from Pokemon Colosseum (you can snag it in the final Stadium). This is just for those you really want to know what Altering cave is, and if anybody wants to prove me wrong, please do. Otherwise, just leave Altering Cave alone. The Pokemon you can catch are horrible, buy Pokemon Colosseum. And if you must buy an E-reader, buy an Eon Ticket as well so you can get the other Lati@s, they are selling them on Ebay for some reason...