Hi Apostolis,
The short answer is that you will probably see more OSPF than EIGRP since OSPF is an “open standard” and EIGRP only runs on Cisco devices. Cisco submitted EIGRP to IETF to become an open standard as well so maybe in the future you’ll see it on other vendor routers and it might become a bit more popular…
You’ll see multi-area OSPF when you have larger networks that require summarization (since OSPF can only summarize between areas).
Also, keep in mind that it really depends on the job what you will encounter. If you work on the internal network of a company you’ll be doing mostly “switching” and some inter-vlan routing. If you work at an ISP you’ll be doing more routing stuff.
Rene