Q8 is from the long selling Q series, uses quadcore hisilicon chipset, 1gb/8gb, android 4.4 kitkat.
this spec is a little low on the memory but should the job well for most apps.
however, 8gb memory... after the os and other requirements, there is only 4-5gb left, can't take too many or very large apps.

H8 Octa is the first one in a new series, uses rockchip, octa core, android 5.1 lollipop.
comes in two submodels - 1gb/8gb and 2gb/16gb.
former as entry level; latter has more memory for more apps.
i believe this model is the current flagship model.

there has been many models in the last 2-3 years of which the most popular were q5ii and q16 - both no longer sold in the market.

for details on specs, differences, best to ask the sellers.

http://www.himediatech.com/productList.htm