You wil probably get as many answer to this question as there are people to answer it... to me that is a good thing.
First of it is a technology issue and second of all it is all about context. If you experienced that launching a missile at around 70mkm you can strike the enemy without retaliation then that should be your long range missils or perhaps a bit more for safety... what is the point with sacrificing speed or warhead to get a better range if you don't need it?!?
The same thing is true for the size of the missiles you use... it always is a trade off between how many missiles you can attack with at what range and with how much electronics etc...
To answer the question more precisely I generally have three missile types in my arsenal. A short range torpedo simply made to engage at very close range, often at beam range depending on the type but they usually have a few million km of range and of mid size. The next is medium ranged missiles that are mainly for escort ships in use as self defence when deployed as patrol or recon groups, this can also be the type of missile you launch from fighters and missile boats etc.. A medium distance are usually depending on the sensor technology and what active and fire-controls fit on smaller ships, that sets the range... could be perhaps 30-50mkm or so... but really it depends allot on external factors too. The third type of missile would be a long range missile, often a bit larger used on dedicated missile cruisers... the hole point of these missile is that it can engage with enough range and enough speed to either hit outside the enemy range or before enemy missiles with good speed (or preferable both).
Missile warfare is often won by the one that fire first or who have the fastest missiles if range is roughly the same, at least if both sides have the capacity to overwhelm the other sides defences. If I have 100 size 8 missile with a range of 100mkm at a speed of 30.000km and the enemy has 133 size 6 with a speed of 28.000km/s then that speed difference can be very important as my missiles will strike first even if I have less missiles overall. There often are an over reliance or focus on these forums on number of missiles alone. If I bring enough glass cannons to the field then the one with the longest range and speed always will win as neither side have any defences at that point, not that I would advice for that strategy as there will always be someone out there with a bigger gun than yours...
If you are already strong enough to wade through and knock out all enemy missiles to comfortably fire short range missiles and knock them out you certainly could have done the same thing from beyond their range too most likely or you just have such a vastly bigger fleet than they have it does not matter what you do... it is when two forces are more closely matched that it matter allot how your missiles perform over that of you opponents missiles.
If you just create missiles intending to fight an imaginary friend you probably will fail anyway and you will need to commit way more resources to do the job than what you initially thought you would or simply waste resources on complete overkill of rudimentary enemy forces.
So... in my opinion taking about typical ranges without any context really does not tell you anything useful from a strategic point of view.
