Well, ideally, the sheet is filled in for you for those two talismen you have, then your choice would be pretty easy. Based on what I've seen so far, the Purple T1 is probably better than the White T2. I *think* that colour trumps tier in most of the talismen.
Each talisman on the previously linked sheet will give you the values by colour and tier at level 1 (initial value), level 10 (1* max), level 20 (2* max), and level 30 (3* max). When enough of the sheet is filled out we will be able to make cross-talisman determinations - ie, which is an overall better talisman, a Blue T2 +15% attack, or a Purple T1 Blind talisman with attack?