Just wondering how people design a new army...
Taking a overall view here I'd have to say both, combined with good sportsmanship. So many idiots tarnish our hobby.
1.) A good list should never lose badly to one type of army.
2.) A list should play to an army's strength, but only slightly if too much of those strengths would detract from an army's versatility.
3.) A list should be mobile (especially for mission capability).
4.) An army should always have a trump card ready to drop to ensure victory.
A well-balanced force is a good start, but if you plan on winning more games that you lose, you should take care to tip the balance when the time is right.
I know that most folks just want to play fun games in the end; after all, what's the point of wasting all that money if you're not going to have fun, right? But losing gets old after a while. We all have our pride, however large or small it may be. A game is played to be won; bit it is how we treat our opponent that really matters in the end, not what list we're playing.
When purchasing an army, the guidelines above are a good starting point.
Unless you've just got oodles of cash stowed away for the spending, it's better to be able to drop your benjamins into an army that will allow you a competitive edge no matter who you face across the table.
And how will you ever improve if you don't try?
If you only like modeling, buy Reaper.
If you're truly into the entire 40k hobby, at least try to win games. You don't have to be a poor sport to win; just put forth effort, design the best army list you can and take your lumps like a real gamer.
The real fun in 40k is knowing that you're not holding back and neither is your oponent, then getting smashed together after the game, lol.