Surely they will provide a modem with the service. You likely just need a good router - the best I've found in the last few years are the ASUS dual-band AC routers. Fast and rock solid, and the interface is dead simple to use.
Buying a separate modem will start paying off before the two year mark. Renting is a waste of money in the long term.
Separate modems and routers are always a good idea, if for no other reason than wireless technology advances at a much faster pace than modem tech. Your router will depreciate more quickly than your modem, and getting a combined modem/router will mean that both devices will need replacement if, in a few years, you want to update to the latest wireless protocols.
I use an Arris modem and Nighthawk router and my connection has been solid. Since my current apartment can't easily support wired Ethernet to my desktop, having a strong wireless signal is crucial.