OK so to sum up: a mix of bikes is good, but it comes down to preference, just try it out.
For an anecdotal story to put things in perspective, I played a tournament this weekend were Table 1 was:
Eldrad
Baharroth
3x3 scatbikes
2x2 war walkers with BL
Seer Council - 10 warlocks on bikes, 2 farseers
Allied Eldar
Farseer on jetbike
6 Fire Dragons + Exarch
3 scatbikes
It was a nasty list with literally bucketfuls of scatter laser shots and psychic dice, plus hit & run and all the mobility in the world.
Game 1 -- beaten by 72 fire warriors + 2x hammerhead, 2x devilfish, 2x fusion suit, 5x piranha, Ethereal + Fireblade pulse bomb.
Game 2 -- beaten by black templar battle company in razorbacks with bikes and a few drop pods.
Game 3 -- beaten by necrons with imotekh, 2x 5 immortal, 2x 5 wraiths, 9 scarabs, spyder, 3 heavy destroyers, doomsday ark, void shield.
Nobody wanted to face this list, but it lost every time, hah!