Litecoinglobal -> Interesting for Litecoin based assets
Cryptostocks -> Not secure (got hacked), low trading volume (except their own stock), BTCT and Bitfunder have more features and better security -> only use them for Devcoin (Fun)assets
MPex -> Lost most of its trading volume (stocks) -> going down

I think you only need to look into BTCT.co and Bitfunder.
A short comparison:
Security:
- Bitfunder: 2FA
- BTCT.co: 2FA, Yubikey Support, PIN, Manual withdrawals (more Bitcoins are stored in the cold wallet)
Backups:
- Bitfunder: Public asset list
- BTCT.co: Automated backups via E-Mail, CSV download
API:
- Bitfunder: None
- BTCT.co: JSON API, OAuth API
Asset creation:
- Bitfunder: Easy approval by Ukyo, Fee
- BTCT.co: Community based approval (stricter than Ukyo), Fee 5 BTC
Trading Fees:
- Bitfunder: 1-0.5% for buyer
- BTCT.co: 0.2-0.25% for buyer and seller
Feautures:
- Bitfunder: DRIP, Options trading, WebSocket
- BTCT.co: DRIP, Options trading, Android App, Motion system, Public portfolios

It is hard to say on which platform an asset would generate more trading volume, but TAT.ASICMINER launched simultaneously on both platforms and sold so far 34,000 shares on BTCT.co and 9,500 on Bitfunder.

*DRIP =  Dividend reinvestment program
*2FA =  2-Factor authentication