I would like to know based on what criteria you think that Sonic made a poor judgment with the ZTE modem ?
Consumer grade network equipment (regardless whether you are talking about dsl/cable modems, routers or wireless gear) has appallingly poor quality regardless of brand.
While yours is far from the first report to indicate a problem with a ZTE modem we also had posters in this forum indicate the ZTE worked better for them.
In my experience with DSL modems the main reason for erratic or poor performance, randomly dropped connections and early equipment death is heat. Despite the fact that most modems produce sufficient heat to get uncomfortably hot they generally do not contain any active cooling (fans). To make matters worse, the majority of dsl modems even fail to properly perform passive cooling by allowing sufficient airflow through the case (factors such as an "elegant" design and "compact" form factor are more important to the designers then longevity of the product).
When it comes to heat (universally the enemy number 1 to all electronics) the user however plays as important a role as the device manufacturer. Putting the DSL modem in direct sunlight is a big (but not necessarily obvious) mistake and so is placing the modem somewhere without or with insufficient airflow (all it takes is a single piece of paper laying on top of the dsl modem to prevent any release of the hot air inside).
I always make sure to inspect modem cases to see where are the actual openings that allow air to enter and leave the case. You would think that manufacturers would choose those openings in such a way to allow bottom-to-top airflow (hot air rises) through the inside of the case (going past the circuit board with its hot components) when the case is standing on its feet or is hung as designed on a wall mount. However with some modem cases I found it necessary to place them in a different orientation then intended by the manufacturer to ensure that all important bottom-to-top airflow through the modem.
In other situations I made sure to place the modem into an active air stream for even better cooling. This doesn't have to require additional expense, in some cases I simply put the dsl modem near a computers exhaust fan.
My current dsl modem (Comtrend Nexuslink for Sonic bonded Fusion) has a USB port and I use that to power a laptop fan under the modem. In this particular case I didn't wait to see if it too had heat related reliability issues, I added the cooling as a preventative measure.
Whether you choose to buy your own replacement modem or opt for the modem rental is totally up to you (I think both are reasonable options). However regardless of that choice I would recommend to look whether anything you did with regards to modem placement may have contributed to an early death by not providing sufficient airflow for cooling.--
Got some spare cpu cycles ? Join Team Helix or Team Starfire!