1) Cost, how much of a hole is it going to leave in my wallet?
2) Does my force look like a real detachment, i.e. is it 'realistic in context'?
3) Does it look cool?
4) How much whoopass is it going to dish out?
Now cost wise an Attack Bike is
£15ish and a Land Speeder £18ish so the Attack Bike at first
looks like a winner, however you seem
to get a lot of cool accessories with the Land Speeder and more options (more on this later)
As far as in being realistic in context, either of them could fit in with my army theme. Maybe the Land Speeder is a little more Blood Angelesque (tm).
Looks wise I used to hate the current Land Speeder model however over the years it has grown on me. The Attack Bike still looks as cool as it always did.
Now onto the Whoopass factor, the Land Speeder has a couple of advantages over its land bound cousin. it is a skimmer, it can deep strike and it has more weapon options if an upgrade can be afforded. The Attack Bikes main attraction here is it is cheap.
After all this I can not make up my mind, I seem to be leaning toward the Land Speeder but it would be far to easy to load them up with extra weapons and spend more points on them than I want.