I was curious, so I looked into the closest analogs of the current revealed Bestow creatures and compared their Bestow costs to the appropriate Aura. Here's what I got:
7 CMC Celestial Archon -> 4 CMC Angelic Destiny
+4/+4, First strike, Flying.
6 CMC Spearpoint Oread -> 1 CMC Shadow Lance with 1B pump
+2/+2, first strike
5 CMC Observant Alseid -> 4 CMC Auramancer's Guise
+2/+2, vigilance (slight difference as Auramancers Guise gives +2/+2 for each Aura)
5 CMC Nimbus Naiad -> 2 CMC Spectral Flight
6 CMC Cavern Lampad -> 3 CMC Vow of Malice
+2/+2, intimidate (Vow of Malice makes creature unable to attack you or planeswalkers you control)
4 CMC Leafcrown Dryad -> (closest match) 2 CMC AEther Web
+2/+2, Reach (Aether web had flash, gave +1/+1, and let enchanted creature block creatures with shadow)
7 CMC Purphoross Emissary -> (Closest match) 2 CMC Madcap Skills
+3/+3, cant be blocked except by two or more creatures (Madcap Skills only gives +3/+0)
6 CMC Thassas Emissary -> NOTHING CLOSE
+3/+3, when dealing combat damage to a player draw a card
4 CMC Nighthowler -> 2 CMC Exoskeletal Armor
+X/+X where X is the number of creature cards in all graveyards
So, approximately, you're paying 2-3 more mana for your Bestow creature to come back as a creature. I'm not sure if it's worth it yet, but I just wanted to put this up.
I guess I should point out that the CMC for the Bestow creatures is their respective Bestow cost, not actual CMC.
Some bestow seem really high casting cost yes they are coming back as creatures witch is great if you board wipe. But if we are talking about standard I think the only one that could actually see play as a bestow would be the nighthowler.It doesn't really help at all though when the format at the moment is extremely fast. And will stay that fast till RTR block rotates out.
Holy crap, I was going through the Columns on the WotC site and found an article on Bestow. He mentioned Evoke and I realized, it's the exact opposite of Evoke.
Take Mulldrifter . For 4U, you draw 2 and get a 2/2 with flying. Or, you can pay 2U and you've played a Divination that may have triggered an ETB effect you had on the field (Soul Warden or Warstorm Surge come to mind).
With Bestow, you can pay 1G for a 2/2 with reach, or pay 3G to give another creature +2/+2 and reach. And, if it dies, you get your bear with reach back.