Of course, each individual in witchcraft and spellcasting can be quite different: for example, something you struggle with, another person might find extremely easy. And vice versa. However, I also completely agree with Hexen. Spells that require you to exert more energy, complex chants, more preparation- most would find to be more difficult.
I'd suggest you start with what spells you feel would come to you more naturally and you think you would use with frequency. Take into consideration what areas of magic you are more interested in and you feel you would connect to.
Remember, thought and feeling are powerful. They are the most important tools, in my opinion.