One important thing to note: There are no rules governing who may join the various guilds and factions. If you choose your class skills wisely, you can max out your character's most important attributes (whatever they happen to be to you) relatively quickly. For example, heavy use of blade will increase your strength. Remember that your skill choices will correlate directly to your attribute growth as well.

Conversely, if you're looking for more of a challenge, you can put skills like athletics and acrobatics (both of which, I found, were hard to do simultaneously) in your custom class. If you are not modding the enhancement system, my strongest advice would be custom classes! Look at the defaults - they're pretty decent, but often they use certain skills to level that you may not want/need with the type of character you're playing.