Setting up internet advice

Actually there's not much difference. You can choose between Vivacom, Mtel, Telenor, Blizoo and at least 2-3 others.
All of these are good, just select the appropriate package of services.

Whenever I move somewhere new, I ask my neighbors what they are on and whether it is any good, as it usually involves the fastest/easiest installation.

Also, keep in mind a lot of local companies in Bulgaria are offering fiber at low costs, so if a good speed is important, ask around for smaller local companies instead of the bigger ones. (I'm not in Plovdiv, so I don't know the names of them). Definitely shop around, as prices can vary. My mother-in-law is paying around 50lev a month for a slow internet and tv package (through vivacom) whereas we're paying 30lev a month for a high-speed fiber connection and television package because we went with a smaller, local company.