NinjaTrader can run as many strategies as you want (or your computer can handle). The main downside there is that each strategy runs on one instrument, but you can have as many strategies as you want, it's just annoying to have to manually start 100 strategies (if you want to run against 100 stocks).
OQ supposedly can run multiple strategies but I don't know how to get that running. It seems like one workspace = one strategy and you can only have one workspace at a time but this is probably a limitation of my understanding (like others have said the documentation for OQ is poor). OQ crashes on me too (especially when re-running a strategy against multiple instruments).
As far as i can tell, neither Ninja nor OQ handle starting/stopping/errors gracefully. You'll have to program synchronizing your strategy with your current portfolio yourself.
I'm just looking for a stop gap until I can write my own and so far I prefer Ninja.
Amibroker doesn't handle automation well (from what I hear), OQ has some annoying quirks and limited support, CoolTrade is not flexible enough for a 'power' user, Ninja does not support advanced features that you might want in the future (according to sky123987). I'm going to look in NeoTicker, TradersStudio, and TradingBlox next.