#1 i'd have to give to fatality. back in the day they held #1 f2p for as long as i can remember, even gave birth to a top clan of that time period too, cp. even though cp was always ridin fi's ***** on trips lol. anyway they were #1 back then for years as i recall, and still today they compete with huge numbers too (minus the massive slump they're currently in).
#2 Tlp, mainly due to thier leaders. hiei hit the charts like a beast, and so did finnald, it quickly gained momentum and became an extremely well known name throughout runescape. i remember back when i was clanless pking at edge, i'd pull off some beastly combo and have people asking me if im in tlp. today they've still maintaned p2p superiority and has always been quality over quantity, just like thier founders. had thier ups and downs, but still a top class clan. unique in it's own way too.
#3 Foe, they've been #1 p2p for a real long time, and also has it's own history. personally i don't know too much about foe's history, as i never really did care for them TOO much. and back in old wild the most i heard of them was 'they're allied with tlp'. this might be real dodgy info but that's just what i heard way back when from others, so dont quote me on it.
#4 Mm, they have insane history, being the first pure clan in history. mm was also the reason why TLP was born in the first place, because the TLP founders were sick of being teamed by them. though the history is behind them, i place them 4th of the top four because the only reason thier founder mahatma was so well known is because he was before his time, the first pure to make a vid with barrage. i believe mm has always been quantity over quality, it's also been proven to me too many times in my own experience, and i value quality. not trying to sound like an ******* but every MM encounter i've ever had in the wilderness while PKing has always been easy kills for me :/ idk what it is but MM just doesnt have the quality for some reason.
this is strictly my opinion from what i've seen through the years, trying to be non-bias as possible. there are probably things i'm missing from each clan, but lets be honest who pays that much attention to everyone to know thier whole life story.