I can give you a few facts here:
- Currency pairs tend to trend, their distribution of returns shows fat tails and their price series show autocorrelation. I advice you to run statistical tests before you "believe" a trend exists.
- There are many ways to define a trend but you can look and test if a price series statistically resembles a random walk with a drift component. This will tell you the likelihood with which a trending component actually exists.
- Hurst exponents and auto-correlations, these two are very important when measuring trend strength. You probably need about 10+ ways to measure trend statistically to make accurate decisions.
- I worked for a large bank, we tracked +90 instruments from which we had +20 FX pairs. From these the best were pairs from Latin America, etc. Exotics sometimes trend much more than major currency pairs or crosses.
Finally. I advice you to learn statistics, if you don't, take a course on coursera for God sake. It will really help you out.