My preference is elective or ultimo. NEVER go elective if your realm has any cultural or religious diversity though - electors won't vote for your heir.
Ultimo is simple enough to manage: make sure your wife Is about the same age as your character - typically the last child will be born no later than 35-42yo due to fertility rates, most characters die around 50-65. If done properly you will have a young adult character and long reigns or at worst a short regency of 2-3 years.
Switch to hunting focus if you need to extend your life expectancy to avoid a regency, switch to rulership if you want shorten it to move to your next character (very likely to pick up stressed or depressed).
Ultimo is simple enough to manage: make sure your wife Is about the same age as your character - typically the last child will be born no later than 35-42yo due to fertility rates, most characters die around 50-65. If done properly you will have a young adult character and long reigns or at worst a short regency of 2-3 years.
Switch to hunting focus if you need to extend your life expectancy to avoid a regency, switch to rulership if you want shorten it to move to your next character (very likely to pick up stressed or depressed).