Can do if you have the equipment - both work well.
Can also do ladder work to work on footspeed, again: if you have the equipment, and hurdle work (though kind of comes under plyometrics!).
Personally i think you should do strength training like Squats, Deadlift, VBench and OH press for a good 6 weeks and then switch to pwoer training like Clean & press, jump squats which will really help with power.
In the off season i am trying to improve fitness as well as speed and i've been doing an 8 week running progmramme to get me running more as i find that seems to help fitness a lot and when my legs arn't as tierd i run quicker in a match as i have more energy.
This is what I am trying to do. Improve my lactic acid resistance within my leg muscles
thats what i need cardio and something to build up the lactic acid resistance so that i dont feel worn down within a match. once i get a free week im going to embark on a massive training program.
Monday - Shoulders
Tuesday - a short jog
Wednesday - Chest
Thursday - also a short jog
Friday - Back and some resistance training (use of sledges and ladders)
Saturday - more resistance training down the rugby club
Sunday - rest day
......I'm not seeing a leg day in there...
Please please don't say you're not doing squats?
What so I can't walk the next day ;(