As you can see from the results below, using java.lang.Math is faster for floats than for doubles, and faster than FloatMath. Furthermore, FloatMath has no .exp() or .pow() prior to API level 17.
On a Samsung GT_i9295 (4.2.2), 2^24 cycles
Math.exp(D) Total: 7405 ms, Per Op: 0.0004414 ms
(F)Math.exp(F) Total: 5153 ms, Per Op: 0.0003071 ms
FloatMath.exp(F) Total: 8533 ms, Per Op: 0.0005086 ms
No data for Math.sin on the samsung because it has randomly decided to ignore Log.d() >:(
On a HTC Hero_HT99VL (2.3.7), 2^12 cycles
Math.sin(D) Total: 42 ms, Per Op: 0.0102539 ms
(F)Math.sin(F) Total: 33 ms, Per Op: 0.0080566 ms
FloatMath.sin(F) Total: 38 ms, Per Op: 0.0092773 ms
Math.exp(D) Total: 56 ms, Per Op: 0.0136719 ms
(F)Math.exp(F) Total: 47 ms, Per Op: 0.0114746 ms
FloatMath.exp(), .pos() and .hypot() require API level 17