Yes, it really depends on the network, installer and traffic, so you need to test both options.
Revshare works so that you get your share (usually 60-75% of what advertiser pays the network) each time someone accepts an offer. With fixed rate, the network is willing to pay you a fixed amount (let's say $1.00) each time someone accepts all 5 offers. So if your traffic finishes the installation, and the installer is clean, then usually the fixed rate is better. But let's say the third offer in installer is spammy and users cancel install or is detected by AV and a lot of installs don't get finished - then better to go with the revshare to get paid for as much offers as possible.
In my experience it works different for networks. For example, when i started with Revenyou's fixed, it worked much better than their revshare, whereas with Amonetize I quickly switched from fixed back to revshare cause I was getting much less paid with their fixed (seemed people were not finishing the install).
Networks also don't want to earn less regarding which method you choose, so often it might even not make a big difference in the end. Also terms for fixed vary, some need to get to half of install, some need the install to be finished. It depends on the installer as well as your traffic. That's why it's best to test yourself.
