For me this Samoan side looks very strong and can be the team from the minor pools to make the semis. They are full of NRL and SL players and they are top performers not bit part players. The likes of Solomona, Lautiti, Carmont, Hansen, Vagana, Meli and Talua are familiar faces to Super League and they are all capable of turning a match.
Tonga on the other hand were far from impressive in their narrow in verus Ireland and they have discipline problems that don't seem to be able to be controlled.
I toyed with the thought of recommending Samoa -6 but the bookmakers have started to see money in the Samoan direction and the best price out there is now 1.83 as opposed to the opening 1.91. It's still not the worst bet in the world but taking 1.44 for the outright is a shade of better value for me.
As I type there are bigger prices on the exchanges for both the -6.5 and outright lines so that may be the place to go before the money disappears. Personally I have layed Tonga +6.5 @2.1 and have taken as much as I desire which obviously translates to a back price of the more normal price of 1.9.
It's certainly worth paying the exchanges a visit and putting up a desired price as more often than not you will get matched higher than the high street if you can form an opinion and get prices in early enough.

Pick: Samoa 3pts @1.44 with Stan James or Coral
 
the man