In terms of boarding I'd opt for the fewest rules as possible.
Having more hits than the average ship type is a nice method, it also gives better critical repair and ramming.
Certain contact weapons that could be used in addition are nice, such as massive claws and feeder tentacles(neither used in the shooting phase). I've toyed with the idea of having these weapons add a modifier for how many points of damage they cause(but this is like doing double damage, so I dumped it).
Re-rolling the boarding dice(or rolling 2 take the highest) is nice and unique, either this or as a standard boarding modifier. I prefer the former
Having Nid ships count as BMs as Sig suggests is good, although always adding the turrets is good as well. I prefer the later but they are both worthy.
I've never liked double boarding and would rather it wasn't involved.
![Grin ;D](http://www.specialist-arms.com/forum/Smileys/default/grin.gif)
***In my rules I've made it impossible for Tyranid escorts to initiate boarding actions, instead they'll have to rely on feeder tentacles or massive claws for contact kills. The reasoning behind this is that they aren't biofactories like Hiveships(capitalships) and as such will try to avoid doing something they are unsuited to do. But then I don't have an instinctive behaviour chart in my rules.
Cheers,
RayB HA