which of these three would be the best for my s-10 truck?
 

Vehicle is a 1999 Chevy s-10 with the 4.3 v6. I'm thinking of three things that may improve MPG a little bit, but I would only be able to do one to begin with so which would give the biggest bang for the buck?
a) front spoiler
b) lower suspension
c) bed cover

I know there are other things that could be done but I'm just interested in which of these three would be considered the best.
Thanks!

I'd say bed cover. Or even better, aeroshell.

Why not all three? Or at least just the air dam and cover... lowering it reduces truck functionality and effectively turns it into a slow, inefficient car with a big trunk. At that point the best mod you could do is remove one of your lugnuts, screw a fuel efficient car onto it, and discard the leftovers.

By the way, wait4meperformance.com is selling tuned PCM's for S10's for $160, no core needed - many folks are reporting significant fuel efficiency improvements (the more credible claims are of 1-2 mpg up from a 16mpg starting reference on 4wd S10's) from this practically plug-and-play upgrade. Wait4me uses EFILive to load custom PCM tunes in and can enable features not present in your stock tune, such as disabling the A/C compressor when defrost is selected, disabling a/c compressor under heavy throttle, reducing shift overlap, increasing rate of O2 sensor sampling & fuel trim (to more rapidly compensate for temperature, fuel variations), ... all sorts of stuff. Even enabling E-fan trigger to allow you to easily fit an electric fan & ditch your engine driven one.

well like i said i could only do one to begin with, but thats not saying i con only do one ever. just picking a starting point.
for what i use the truck for, which is to carry bulky but not heavy items, lowering won't have a negative impact.
thanks for the info on the pcm stuff, thats definetly worth checking out.

Been there, done that. Best first move is a bed cover if you can live with it.

I'll agree with the others and say that the bedcover will probably yeild the best results...if it doesn't compromise the usefullness of your truck.

I think my rubber belting front spoiler(pics in my album) smoothed out my front bumper and helped a little, but I haven't done any a/b/a testing to prove for sure.

I am seriously contemplating lowering my truck a little when it comes time for new tires and an alignment. The torsion bar crank on the front doesn't seem too bad from what I've read about it, so long as you get an alignment done also. Lowering the rear a little will involve a different set of springs or some type of lowering blocks...I haven't done enough reading up on this yet.

Definitely a bed cover, mine didn't see any noticeable improvements when i lowered mine. Dropped it 4/6. Although, mines a fullsize.

belly pan, take a look under the truck then look at the back of the truck, the bed will look smooth and aerodynamic in comparison.
if you don't need the truck bed then sell the truck and get one with a smaller engine.

I'd have to agree that the bed cover is probably the single best mod of your list. However, it would be about equaled by a front grille block (if you haven't done it). And a grille block can be done on the real cheap --without looking bad.

Get a front skidplate, and extend it with plastic.

Also, build a wind deflector for the rear axle. Maybe going from the center out to the edges of the tires?