first of all the best forex EA are using scalper strategy and many excellent and verygood scalper EA's like forex bulletproof, kangaroo, primeval, scalper EA and many others.

1- your should choose ECN/STP brooker like IAM FX, ATC Brokers.( i trade with them live they are the best).
2-you should choose the EA with good income and low draw down and steady performance smooth upward trend .
3- you should choose forex robot with 60 days money back granted to test it live on these period.
4- you should choose the best hosting provider iam using forexhoster.com its costy 69.69$/monthly but good there are many but i use this one only.
5- if you feel that you EA performance slowdown update it or stop it and use other one .

all EA should be updated from time to time to maintain the same performance.

Regards,
Suhail