I have always happily paid the full agent fee (but we let the agent work for it).
Remember, the agent is NOT getting the whole fee, just a percentage, the rest goes to his company/boss!!
If the agent doesn't deserve the full fee you should look for a better agent.
Remember: you pay peanuts, you get monkeys.
Otherwise I agree, you need to do the homework (online) but then you really need to invest the time to go out there and look at flats (online is always outdated in HK). We recently rented in Sheung Wan and probably looked at 15-20 apartments (both in Sheung Wan and Midlevels which we were also considering). But we did tons and tons of online research and thinking.