hey, do you know why airplanes have different wing tips? i've always wondered that...
The spirals are basically vortexes generated by upward airflow travelling up from the bottom of the wing. Certain wingtips and winglet-type devices change how those spirals form, and how strong they are. Every aircraft has a different aerodynamic profile so some benefit from different types. Additionally, the difference between raked wingtips, blnded wingtips, and no wingtips is that:
Raked wingtips are heavier and require wing-reenforcement because it fundamentally increases wingspan length. They provide the most efficiency over longer, TATL or TPAC, routes (hence why they're on the 767-400ER, 787-8, and 747-8i).
Blended winglets provide minimal wingspan length increases... and require less reenforcement. They are, however, not as efficient on longer routes... and are best used on medium-range routes.
No winglets are best on short routes. Winglets are heavy and add weight. Those increases are nullified if an aircraft flies on short routes.
Some aircraft, like the 767-300, A330, and 737-700/-800, would benefit from raked wingtips but then due to to gatespace requirements, those become an impossibility. The 767-400ER can get away with raked wingtips because it was designed to replace the L-1011 and DC-10 (both of which had larger wings than the 767 base models).
Hope I didn't overwhelm you.