Both have pros/cons
Suburban
PROs
Major components are accessible via outside compartment (Both sets of T-stats, gas valve, electric element, anode rod)
CONs
AC & DC Junction Boxes on backside along with circuit board which does not have a Fuse and combustion/exhaust 'U' Tube is stacked so unequal surface contact for heat transfer, Steel glass-lined tank which can not be replaced, NO air shuttle to adjust air/fuel ratio
Atwood
PROs
Aluminum Tank/no anode rod, gas valve accessible, thermal fuse protection, air shutter, diagonal combustion/exhaust 'U' Tube for better heat transfer, Fuse protected circuit board, NYLON Hi Temp/Press drain plug, replacement tanks available
CONs
Only one set of t-stats for both AC/Gas operation, DC Relay and AC Element on backside of WH Tank
Both Brands are functional, do what they were designed to do and are roughly equal in easy of use
For me it's a toss up
Whichever one comes in the RV I purchase is fine!