We currently use 3.4.4 as our standard image for our ASR1K's, as that's the latest MD release, and we need a stable environment.
If you need a feature that's only available in 3.5 or 3.6 release then 3.4.4 obviously won't be enough for you.
What part of the base config are you interested in?
AAA? SNMP? BGP?
Most of the part it's pretty straight forward, except AAA.
I typed a command that we've been using for years; was told by IOS-XE that it'll be deprecated.
But when removed AAA wouldn't work right.
I ended up just leaving that legacy command there just to get the darn routers deployed in time.