Quick calculations for my reference since I was curious about the actual numbers... Spark is about 6k exp (3k soldier+450 times 6 members) for 8 AP. An enhancer 3 is 27k exp. So spark is better unless you want to save AP and buy the AC directly. On the other hand the advanced daily (the 30 AP one) is probably more efficient than spark. 4 shots of spark is more AP but less exp than a single enh 3.
Farm ac like there is no tomorrow (4ap breezeway/ 8ap prelim contest), challenge recruit, feed enhancers.