...And at the end of the day, it's still an AV11 open topped skimmer....
the FW variant is worth the extra 10pts on top of the standard because its weapon is t-l and its AV11
Correct me if I'm wrong but I believe the Piranha also has a front Av11. However the XV-42 has a closed top so it doesn't suffer the open topped rule I'm not sure how much this improves the survivability or points efficiency, but it's a minor improvement on the standard Piranha which may explain any additional expense.
I'd also like to point out that in it's description on the FW website they state that it was designed as a support unit for other 'armoured units'. This suggests that the original intention of the designer was that the TX-42 be used in support of Hammerhead Gunships in a fast moving Mechanised force (which frankly makes me more interested in buying them). As opposed to the Piranha light skimmer which appears to have been designed as a support unit for a mainly Static/Hybrid force. IMO as a fast moving, rapid response heavy weapons platform used to provide special weapons response for FCWs. Presumably to alleviate some of the pressure from Crisis Battlesuit teams and/or provide a faster response mid to late game.
My point is a TX-42 might be better placed to support a fully Mech non-crisis force than a Piranha and they would appear to be a 'fluffier' or at least a better fit for a themed Mech force... Damn those boys at ForgeWorld. Damn them all to hell!!!
Why do they need to keep making such good sshhhh... stuff?
As for the 'best weapon' I personally fancy the Missile Pods. I could see two of these and an Ionhead supporting two Railheads in a Mech themed force very well, but that's just me... muhaha!