I prefer the ball reviews of BJI currently. Previously I lived and died with BTM's reviews, but they seem to have lost their way with respect to accuracy.
Stacked leverage drillings are no longer relevant and their definitions of dry, medium and oiled lanes seem to deviant from the average by far too much and that skews the view of each ball review.
Both are worth subscribing to for their wealth of good articles of the various aspect of bowling. I will not cancel either one for quite a while.