the final results were definitely the most influenced by differences in slippage. Also spreads (commission) and spread widening played its role (that is causing Stop-Loss hunting, executing market entries / exits at worse prices, or not filling TPs). There are simply so many factors that influence the final results, and the only way to truly compare brokers and choose the best one is comparing results from real accounts. Of course, beside final results - security of deposits, trustworthy and fair broker's approach are also very important.
Exactly - I wouldn't say that it's a rule, but usually brokers that won't process withdrawal request have very bad trading conditions, so anyway it is usually not possible to make more money with with them.