With a good end to the year (25% fewer homicides in December), Guatemala ended with a homicide rate nearly the same as as 2012. In 2013, the rate was 34.0 while in 2012 it was 34.2. Guatemala's murder rate is still very high but obviously much lower than the 46 per 100,000 it recorded in 2009.
In neighboring El Salvador, authorities registered 104 fewer homicides in 2013 compared to 2012. It was actually the least violent year since 2003! La Prensa uses 2007 population estimates to illustrate that the murder rate dropped to 43.3 in 2013 but using the 6.2 million population estimate it is 40 per 100,000 - about 30 points lower than 2011 (the year before the gang truce).
Honduras finished the year with a murder rate of 83 per 100,000 which is 2-3 points lower than the last two years. Those numbers are from UNAH.
Given the uncertainty surrounding true homicide numbers and reliable population estimates, I'd be comfortable with saying that there was no change in each country's homicide rate but, if pushed, each country experienced slightly lower rates compared to the previous year.
Belize walks away with the most improvement cutting its homicides from 145 to 99 for a murder rate of 30 (down from 44). There's no doubt about the homicide rate here.
Here is a chart on homicide rates for the four countries since 2000.