What type of housing is best for a longterm stay in Eastern Europe?

Longterm meaning 2 months.

Apartments, hotels, hostel, bed and breakfast.....?

I don't want to spend too much but I don't want to be too uncomfortable either.
Sofia, Bulgaria

it all depends where exactly you are going. which country, and is it in the city?

Depends on where.

Apartment prices are quite reasonable, and finding short term leases is possible. Here's an example of a short term lease company so you can get an idea of prices and stuff: http://www.nest.hr/eng/index.php .

Just search around on google, many expat sites have listings for apartments in English.

If you are really looking for something on a budget you could try hostels, arrange in advance and you'll probably get a discount.

better an apartment but we need more details