I'll second what California98Civic wrote:
If you want to optimize your mpg, get a manual transmission.
Here's a link to the EPA's page for the '97 Civics.
EPA page for 1997 Civics
The HX w/ automatic is the first one at top of the list; you can recognize it by the continuously variable tranny.
29/31/35 mpg: city/combined/highway.
The HX w/ standard tranny is the first of the manuals listed.
31/34/39 mpg.
Both cars show they have the VTEC-E engine, if you follow the link for the individual car's page and scroll to the bottom where the engine is ID'd.