A standard character format protects the words in the trademark for any font, appearance, color, stylization, etc. Accordingly, in theory the protection afforded to a standard character mark is much broader than that afforded to a stylized mark.
In regard to which and/or how many variants should be applied for, this is most likely a business determination based upon the amount of resources you wish to devote to the protection of your brand(s).
For instance, Nike may apply to register the slogan JUST DO IT alone, the Swoosh symbol alone, as well as the Swoosh symbol and JUST DO IT underneath the same to maximize protection. But Nike's economies are significant compared to the cost of a trademark application.
So determine a reasonable budget for what you can afford to invest in the registration of your marks and once you figure out the cost of filing for the same (government filing fees, private law firm or filing company services) you may then decide which marks should be applied for within your budget.
Hope that this helps,
/Matthew H. Swyers/
The Trademark Company