The longest range version of the Tomahawk anti-shipping cruise missile, deployed in submarines and on war ships for it's long stand off range, when they were being deployed.

I choose the tomahawk because of it is long range, should be as accurate as other tomahawks and it is big and packs a big wallop of a ship wacking war head.

Not sure if it is still in use, as I have heard in other posts they have been withdrawn from service?

The other western missiles each have their strengths and weaknesses, but the tomahawk in it's hayday seemed to hold the most aces when stacked up against the rest of the world.

You have the most prolific, the French Exocet which can be fired by aircraft, missile gunboats and even launched ala hizbolah from the back of a truck. It is effective to some extent, but has been known to miss or near miss it's target and often the warhead does not even work, the damage is often caused by the unused missile fuel.

Harpoon that should be the 2nd best compared to the tomahawk, can be launched from all platforms, is known to be deadly and accurate with a sea skimming and pop up and dive down attack, known to be lethal, still in use by the US and all allies that buy US armaments. Unfortunately it's range though extended and improved cannot be compared to the tomahawk, though both are subsonic missiles, and today it's range and slow speed make it loose out to the longer range mach 2 plus soviet block missiles.

Kommaran, should be the most deadly german anti ship missile or for the whole EU, 20 shaped warheads to better devastate a ship, launched from aircraft and ships, but again the range is rather short. A small missile that packs a multiple punch,  I wonder if the missile were to strike a  small  gun boat, of the 20 independent shaped charged war heads, probably only 10 might blow up in the target, while the rest of  the other half would not get to detonate if the missile is designed to bore through ships?

Penguin Norwegian anti ship missile, good and affordable, but being an infra red missile with a small war head that is more suitable for aircraft launch, such a weapon can best be compared to the British Sea Skua, am not too sure if it may be launched from ships. And the effectivness of it's missile against infra red counter measures, but a ship is a large HOT target.

Gabriel Israeli anti shipping missiles. Not too popular in it's hey day as an aircraft launched missile due to it's size, but in it's hey day it had many modes of guidances that an operator may have fun switching around with to confuse the enemy, from passive to active, radar to radio? good size warhead, but it is let down by it's range, but when close in to within it's range the old missile could still play devilish havoc on your enemies.

British Sea Skua, as best compared to the Norwegian Penguin, aircraft launched, not designed to sink but to disable ships.
I guess the US navy or marines that operate choppers like the Sea cobra could look into the possibility of utilizing this weapon rather than going closer, but if a hell fire works???

There might be more obscure western anti shipping missiles out there that I do not know about, but this about does it, and the reason why I picked the tomahawk was that it would really be a range extender when fired by cruisers and the submarines, really a long range big punch of a missile. No ruskie or chinese tubs are going to be too happy or afloat for long when the tomahawk strikes.

Oh I forgot, if Taiwan is to be considered in the Western sphere of influence and in the fold of the Western allies.

Then the Taiwanese counter to the China made soviet sunburn supersonic missile clones would be the best western missile currently. The US and all who need to counter such missiles should really consider this Taiwanese solution.  Simply the  Taiwanese made these missiles even faster and longer ranged than the China sunburn clones. But with western standards of accuracy and hit probabilities.

Not too sure of the name, some kind of feng, either a xiong feng or some other.

I do know that when the first Taiwanese harpoon clone (also named fierce wind or some sort) struck a barge target in the early 80s, it was the beginning of their mastery of anti shipping missiles over the Chinese. Dramatic vision of a camera mounted on the barge target, and the orange explosion that blew up the protected cam in 3 seconds. There was a huge reaction and STANDING effect. All the Taiwanese  statesmen and elderly  gentleman/roughphian politicians gave a standing ovation. As well as the mainland Chinse communist leaders who also stood up to spit venom, condemnation, jealousy, and threats of destruction, as the Taiwanese missiles would be the spoiler to their shipborne invasion plans.  

Add RBS-15 to the list.

I'd vote for the SLAM-ER as far as current Western systems are concerned.  It has a 280km range and modern GPS/INS + midcourse guidance with terminal IIR homing.  I say this is the "best" due to a combination of factors, including that its range allows it to be carried by platforms that can't operate in high-threat environments, such as maritime patrol aircraft.

In terms of sheer effectiveness, it would be pretty hard to beat a JDAM though.

For some reason it reminded me of the favourite phrase that crops up all the time in the series "Deadwood"

Tomahawk Anti Ship Missile (UGM/RGM-109B TASM) is a quite different missile from the TLAM.  It was not an adaptation of the TLAM, in fact it was developed simultaneously with the TLAM and was operationally deployed before the TLAM was. 

TASM did not have the TLAM's TERCOM system, instead it used an inertial guidance system for long range navigation.  For terminal homing it used a variant of the Harpoon's seeker that was equipped not only with an active radar for terminal homing, but an ESM system for passive radar acquisition of targets.  TASM would be launched in the general direction of the target; when it reached the expected general area of the target, it would fly a search pattern and look for the target using its ESM to detect targets and its active radar to lock on. Once it was locked on, it would fly a seaskimming attack profile, and could pop up or change course to attack from different directions.

The TASMs are no longer in service.  The current RGM/UGM-109E Block IV "Tactical Tomahawk" could possibly be used in an anti-shipping role, but it has no radar seeker and would have to be targeted either via GPS or its onboard camera, which is kind of awkward for hitting moving ships.

Tomahawk anti ship missiles are no longer in service and use.
The currently best anti ship missile would be Harpoon.