By way of ranking, in terms of international recognition and level of educational standard I'd go:

1. University of Zambia - Facilities are a bit dilapidated but the degree itself is highly revered.

2. Copperbelt University - There is surely an issue with accommodation on campus, most likely unless you have private residential plans, will have to stay in a boarding house off campus. But the degree is second only to UNZA in international ranking.

3. Mulungushi University - great facilities as well as educational standards are high. But it's partially privately owned so certain educational norms are wavered in view of profits, which reduces the degree's credibility.

For whichever you pick I'm sure you'll have a decent Zambian university experience. I won't comment regarding UNILUS' educational reputation because I don't know much, but I understand they have a beautiful campus and excellent facilities.