Prince is better: It can be used to improve the demon pool for Guldan to resurrect, and copying doomguard is an easy 3 cost 3/3 charge, or voidcaller as an easy 3/3 taunt that summons 3 voidwalkers. Copying a cube also copies over the deathrattle. You can even copy, for instance, a righteous protector against an aggro paladin for a 3 cost 3/3 taunt with divine shield. The card is just very flexible and always finds some use in any matchup.
Umbra is used for burst. Cubelock doesn't really need burst. However, if you play wild, umbra is more likely is be useful across more different classes and decks.
idk i wanna try the cubelock . and i have enough time to get my dust back right?
You'll have enough time to get your dust back if you buy packs, which is also not a good idea. Start hoarding gold for the next expansion so you can open a few dozen packs immediately and get straight into the next meta, otherwise you'll be behind in the next meta for the first few weeks, if not months.
But if you really want to try cubelock, then go ahead. Ideally, one should start hoarding both dust and gold, but gold is more important, and you'll probably get a decent amount of dust from the HoF'ed cards.Ultimately though, people play HS for fun, so if fun for you is cubelock now, go for it. Not to mention that cubelock will not lose anything, so it'll most likely still be good in the new meta (but I could very well be wrong).