There are various things you will want to bear in mind when you are choosing your volume lashes and the lashes you like may vary depending on which pick up technique you prefer.
Here are the things I consider when I choose my lashes:
If you look closely at some lash extensions against a white background you can see that they have a slight blue or grey tinge to them. For darker, more striking lash sets choose a brand that offers a darker, black lash from base to tip.
Unless you specifically want feathered lashes, look for lash strips that are uniform in length and don't have shorter lashes within the strip.
The kind of strip you prefer can depend on your preferred pick up method. I like a strip to be quite tacky so I can place and make my fan there. However, you don't want so much tack that it sticks your lashes together and gives you a Tbar. If you like to make your fan in one movement then the tack of the strip is not so much of an issue for you.
Most lash extensions are made from PBT but you will find variations in width and surface texture depending on the brand. It is important that you like the overall look of your lashes but it is also very important that they bond well. From my experiences trying out different lash suppliers, I have found some beautifully dark, really perfect looking lashes that fan easily but they do not bond well.
This is something that you should bear in mind but it's more important what the fans look like. I have compared lashes where one appears to be more perfect and uniform in direction on the strip than another. However, once the fan is made I could not tell the difference between the two.
Again, something to bear in mind but not the most important of criteria. A C curl in one brand may be stronger than that in another but if you find a brand that you really like but the curl isn't strong enough you can just use D's instead of C's for instance.