alex7841

Not necessarily.  I have a couple of small tanks that I use lower resistance coils in around the house to get clouds.  In my Mello III (Mazi, I guess, as apposed to mini) I like using the .5ohm coil as I take it out and about and enjoy using less liquid and less battery life.  I still get good taste using the .5.  I find each coil/tank combination has a "best use".  Having said that, I also blew a cloud into the bottom of my drummers kit from a .25ohm coil.  Great fun. He though is sound module had went up in flames.  Watching him try to fan it off was a hoot!

My recommendation - try them both.  Run at least a full tank with each coil, then decide which you like better.  Preferences vary from person to person and opinions on which coil to use are, for the most part, purely subjective.  If it was me, I would run the .3 ohm because I am not necessarily worried about battery life or liquid consumption so it is closer to my personal vaping style.  @Bebop, on the other hand, might prefer the .5 ohm specifically because it will cut down on the amount of liquid consumed and slightly extend battery life.
Either of the coils should give you a good vape experience, though.

They both appear to be kanthal coils so generally you'll vape with slightly higher wattage on the .3.  The .3 will go through juice quicker.  Your battery will run down noticeably faster on the .3.  You should get more vapor on the .3.   As for taste? That's pretty subjective.