It depends.
A+ is a generalist certification covering both hardware and software. It is vendor neutral although it is very MS-centric.
MSCDST expires, A+ doesn't.
MSCDST is a very specific certificaton dealing with XP only. That puts you in a pretty narrow slot.
A+ is an entry-level cert while MSCDST is a little more higher level.
If I might make a suggestion... Get your A+ and then your MSCDST. One builds on the other. and remember, certification is a journey, not a destination.
A+,N+,S+,L+,I+,HTI+,e-Biz+,CETsr,CST,CNST,CNCT,CFOT,CCNT,CCTT,ACSP,ISA CCST3