Another 'in a nutshell' post...
I'm a big fan of big names, they are cheap, one can be given to any character and you can even repeat the same Big Name for more than one character. There are 2 small restrictions :-
1) Only a Tyrant can be given Kineater and
2) only a Tyrant and Hunter can be given Beastkiller.
Neither of these are major drawbacks. Kineater is a waste of 35 pts anyway. The Tyrant will be your General in 2000 pt games (if you take one) so units will benefit from his leadership within 12" anyway.
The Beast Killer Big Name would be best given to a monster assassinator anyway, enabling him to do double wound damage on large targets (providing they're not using a magic weapon)
Rather than going through all of 8 of the Big Names, I will focus on just the 1 must have Big Name. All you need to know about the others is that they are all good value for money, better value than most armies magic items (choose according to your tactics)
The one that really stands out for me is :-
Mawseeker
This is one of the best value purchases you can make in the whole Warhammer Armies Fantasy World.It boosts the character's toughness by 1 but gives him stupidity.
Don't worry about the stupidity, give this Big Name to a Tyrant (probably your 2000 pt army boss or preferably a Hunter which both have a leadership of 9)
You will rarely fail a stupidity test with this leadership, let's face it you should be in combat most of the time so it will not be tested for anyway.
Here's the big news...
The Mawseeker costs only 10 pts !!!!
10 points to boost a character's toughness from 5 to 6 (to make him as tough as most Dragons !) is an absolute giveaway ! I would spend 50 pts, maybe more.
Make sure you use this big name. A Hunter hero who will come under a lot of sustained missile fire throughout a battle will love you for it and be your best friend for life - and you can expect him to live to old age with a toughness of 6 :)