Looks like you've done your reasearch! This is a journey I do every other week - personally, I go for the X53.
It's just over 4.5 hours (often less) to Poole and will cost you £6.50. There are buses every few minutes from the bus station into Bournemouth. It's only about 20 minutes to Bournemouth and will cost you £1.70/£1.80. Honestly, it isn't a bad journey because it goes along the coast and so at least you've got something to look at! Besides, for the price, you can't exactly grumble (but maybe I'm just tight... ha).
Trains? Don't even go there! I've heard it's an awful journey. I've only used National Express once, during the snow, but it wasn't the direct route (took 6.5 hours via Bristol
) so can't comment on that. However, there is only one coach each day to/from Bournemouth. Now, if you got the X53, you'd be able to spend a few hours extra in Bomo and have about 5 squid extra monies!
Wouldn't that be fun!
I don't know if any of that's very helpful, but I thought I might as well give you my view on things. I hope it's of some use anyway