I would always start off with the default character sheet. The benefits of doing so are the following:
Everyone has information in the same place. If a player can't find something, the DM or the person sitting next to them, knows where to point.
It tends to have a certain logic to the layout, maybe related concepts easier to understand.
It takes less time than designing your own.
However, I have also found that sometimes new players will get overwhelmed by the official sheets. This is because they also suffer from common flaws:
- The sheet is designed for all classes, and may have spaces or information that you don't often use.
- It makes reasonable assumptions about playstyle that may not be best suited for an individual who does things differently.
- There is a lot of information and spaces that they don't understand.
- A sheet might be missing places to write out unique spells or abilities or other information found in the rulebook that a player might want to refer to often.
Inevitably, when we play each person has their own style of sheet that they prefer, some found on the web some created by scratch and some made with blank pieces of paper. Often, however, I have found that even experienced players, if they make a quick sheet on a blank piece of paper will occasionally forget where on their sheet they put something. For this reason, I would recommend using well designed sheets, or designing a sheet that makes it easy to locate rarely used information.
Technically a blank sheet will always be the quickest to fill out if one is not worried about organisation, and may allow you to get to the fun part (playing the game) faster. But a well designed and easy to read sheet will be the most fun for the DM and the party overall, as less time is spent searching the sheet and more time is spent playing.