stay away from the ones that aren't water soluble as they do not mix. the ones with red x's aren't a lost cause because you can still try them and they will give you the other end of the spectrum for comparison. (plus they are good dripped into coffee as a sweetener)
and the dark ones. some of the medium shades mix well... but the dark ones are really tough on the atomizer due to their sugar content.
when you do start mixing, if you haven't before, a good test is to mix and then put your drops onto an empty fresh cartridge. If it pools and just sits there, it is too thick. Adding more water helps a bit, but it dilutes the flavor and if you are like me... I don't mind flavor at all. The stronger the better.
oh... and vanilla... there are two kinds of vanilla offered by lorann, clear and dark. go with the clear. You can pick it up at hobby lobby if there is one near you. They also have very small droppers that fit perfectly into the lorann bottles and give you better portion control.
be careful. mixing your own flavors gets very addicting... you get all betty crocker and the next thing you know, your kitchen is cluttered from one side to another and dinner never gets made.
oh... and another suggestion. while you are out shopping, if you don't want to commit to one flavor off of the bat... get the little paint by numbers paint holders that have lids. you can mix very small quantities and play with your percentages to get what you think is the best smoke for you. the lids are nice because they fit tightly and can allow you to shake the mixture really well.