Do you find your prayer life more effective praying by yourself, in a group of 2-4; or in groups of 5+ ?
Or does it make a difference?
Salty
It's hard to say, as each has a different purpose. My personal time in prayer is for my personal growth. Corporate prayer is for our growth as a body.
And how are you defining "effective"? Is it as the charismatics would define it, where God, who they see as a cosmic genie there to grant their wishes, gives them all they ask for? Is it as the Reformers saw it, to know God's will? Is it as the Puritans saw it, to align our will with God's?
Going by your posts in the past, I'm guessing it's a combination of the later two, but that's kind of an important thing to nail down before you ask that question or else you won't get the answer your looking for.