Starting to build up my tools collection, is 110v preferable over 240v?
Does 240V offer better performance over 110V


240V means less losses in wiring which may lead to better performance at the end of long extension leads. Other than that I wouldn't expect much difference assuming the tools are otherwise equivilent (e.g. you aren't comparing "DIY grade" 240V gear to "professional grade" 110V gear). 


  Is 110V considerably safer in worst case?


Debatable. 110V, especially the centre tapped 110V system used on UK construction sites is less likely to give you a fatal shock if you come into contact with exposed wiring. 

On the other hand the lower voltage combined with the use of small transformers significantly increases the risk of a fault drawing a current which is high enough to cause a fire risk but low enough not to blow a fuse/trip a breaker. The use of an isolation transformer also defeats RCD protection unless an additional RCD is installed after the transformer (which is not the case with typical portable "yellow bricks").

So it really depends on the environment. In an indoor workshop I would be more concerned about fire than electrocution (though I wouldn't be massively concerned about either) and would prefer the 240V tool. 

If I was going to be frequently using the tools outdoors in the rain I might make a different judgement.


  If One is "no" and Two is "yes" then why would anyone get 240v?


Transformers cost money, take up space, are a pain to lug around and waste power.