In what context?
Firearms, tanks, helicopters etc are for regular military units engaged in a war - and we can all hope for less wars.
Swords are archaic militarily, far too many knives are used as weapons by street thugs.
If you mean at a personal level the best defence is first of all do your best to avoid trouble, the second is flight if at all possible, third, trying to defuse the situation. Physically, being able to use unarmed combat skills may give you sufficient break to escape the coward who is trying to attack you, or make him flee.
Life is more important than anything else, and although self-defence might be allowed as legal defence in Court, depending on your country's law, killing anyone is illegal!
.......
This post has particular significance in the UK.
Firstly there is a serious problem with knife crime particularly among boys and young men often caught up in drug-dealing gangs (so a double problem there) but also carrying knives for so-called "self-defence".
I do not know how serious this is numerically, but that it exists at all is serious. The Police and criminologists who have investigated it have discovered that those who carry knives are more likely to be victims of others. Why, I am not sure but I assume bravado as word gets around.
Further now, to two nearly-coinciding events.
The first is that machetes, so-called "zombie knives" and similar - weapons made purely for killing people - have just become illegal, after an amnesty inviting handing them in without question.
The second was the trial last week of two boys who used a machete to murder a complete stranger to them for no motive. The victim was 19. The murderers were aged only 12, mere children, at the time. They were sentenced to Life* with a minimum tariff of eight years; but being only 13 now will be in some form of secure juvenile accommodation, not an adult prison, until they turn 18.
Notable in this case was that one boy had had no previous police or social-services record. The other had an awful history of exploitation; and one wonders if, when and how his parents are going to be called to account for their neglect or abuse.
*(Literal "life" sentences in prison with no prospect of restitution and release are very rare, used only for exceptionally egregious crimes by people unlikely ever to repent or be safe to release. In any Magistrates or Crown Court trial the sentence is set at the end of the hearing, by the magistrates or judge; and according to sentencing guide-lines set in the relevant law. A Crown Court might defer sentencing to a later hearing after considering background reports. Neither the prosecution nor defence can call for any particular sentence.)
