Character sheets are a staple of many tabletop RPGs and in my view, they serve two functions: one is to enable you to learn the rules of the game (which occurs when you start filling out the details of the character sheet) and the second is to facilitate play by showing players (and GMs) all the necessary info of their character in one glance (i.e. the filled-up character sheet). Now the dilemma here is that you usually get one or the other. Can both concepts be reconciled? Perhaps but you're usually leaning more towards one or the other.
Now the character sheet in the Player's Handbook falls more along the lines of the former. That's why you have all these forms and boxes to fill up. When creating your first character, you slowly discover the game's rules and details of your character when you start filling it up. However, during game play, it's not the most efficient of layouts. In fact, have you ever wondered why the pre-generated characters used at conventions aren't the character sheets at the back of the PHB? Yes, the designers redesign the character sheets for convention play (and including the one included in Keep of the Shadowfell) as they're focused on facilitating play rather than teaching the rules of the game. Here are some reasons why I find the default character sheet to be inefficient (and many of these points also applies to the previous editions of the game):
1) There's too many boxes. When used correctly, boxes can highlight important portions of a character sheet. Unfortunately, the PHB character sheet uses too much of them. On one hand, yes, there are some items which are easy to find (mainly through familiarity) such as your ability scores (top left-hand side of the character sheet). Others, such as your actual attack bonus, not so much.
2) It's too compressed. We Filipinos have fear of white spaces and tend to fill things up as much as possible. The PHB would make us proud. The problem with too much compression and lack of white space is that distinguishing each section can be quite difficult.
3) No room for details. Choosing your character options (ability scores, powers, feats, skills, etc.) in my experience has been quick and easy in D&D 4E. Writing those details down, on the other hand, takes some time. The character sheet, unfortunately, does not really give us space to write down the details of your various powers and feats. It's more of a list rather than a summary of your abilities.
Now I'm not criticizing Wizards of the Coast for the character sheet in the Player's Handbook. As I mentioned before, this is a design choice, on one hand used to help teach players learn the game, and perhaps on the other hand a sacred cow. However, compare that to the character sheet used in Keep of the Shadowfell:
1) You know where each section is. It transitions from your HP to defenses to attacks, miscellaneous abilities, and finally your powers.
2) The character sheet has room for lots of description. For example, the abilities of each power is described. The same goes for your racial traits, your feats, etc.
3) The powers are color-coordinated. This makes identifying which powers are daily, encounter, or at-will.
4) There is a clear hierarchy of details. Let's face it, Keep of the Shadowfell was mostly designed for combat. The character sheet reflects that as most of your combat-related abilities are in front. The not-so-important abilities (skills, equipment, ability scores, etc.) are relegated to the back.
Now comparing the two character sheets together, honestly, which one is easier to use during game play? Of course the weakness of the latter character sheet is that it really isn't customizable unlike the former in which a pencil and an eraser will do in a jiffy. There are two design goals in play here but during games, ease of play is my top priority.
Personally, I use my own variation of the Keep of the Shadowfell character sheets. You can find them here. During my actual sessions, I find that players who use that character sheet as opposed to the ones using the PHB character sheet make decisions quicker. No need to reference books and the like to find out the details of your character's abilities. It's all listed down. Unfortunately, this also entails more work on the player's parts as they need to type their character then print them out.