My suggestion if you have a soaring operation close by that will allow
you to fly reasonably often with reasonable expense then do the glider
1st.

If you have to travel or availabity or cost are issues then I would
recommend at least going up to Solo in a power airplane. You can learn
a lot a lot of basics of a flying in a few hours of power instruction
and power instruction is typically easier to locate and schedule. If
you can find one, find an instructor that teaches both glider and power
(rather hard to find I suspect). At the very least let your instructor
know what you are planning, they can help taylor your instuction to
your goals.

Having the skills to solo a power airplane will greatly accelerate your
progress in the glider. However if the glider/instructor/towplane and
tow pilots are all readly available and reasonably priced then go
glider only.

Brian
CFIIG/ASEL
HP16T
Boise, ID