You won't find a single SIM card enabling affordable data use in all three countries. For Germany the usual recommendation is Lidl (for detailed info see
this wiki and
the Lidl thread on this forum.
Depending on how much data you need in Switzerland I would either recommend
Swisscom's "Natel Easy BeFree" (CHF 4/day for unlimited data) or
ok,- mobile (300MB for CHF 7/month or 1GB for CHF 15/month). The latter are sold by most "k kiosks" scattered all over Switzerland (including airports and train stations).
As of Austria hopefully another forum member will be able to advise you. However it may help if you provided an indication of your expected data demand.