UPDATE:
A couple of days after I did the Reset All Settings option (back on Saturday), I found that things reverted to how they once were, i.e., not syncing immediately/taking forever to sync, leading me to make a change in one of my tasks to force a sync/refresh. As of last night, I had about 66 reminders in total, spread across ~10 lists and decided (not as an attempt to fix the sync issue) to reduce the number of lists that I had (it was just too many); so, I ended up reducing the number of lists to 3 and now have about 55 reminders in total. That said, ever since earlier this morning, I've been able to sync without any hitches across all my devices: iPhone 4S, iPad 2 and Macbook Air (2013, running Mountain Lion). I've done several tests and so far and it seems to be working great - I even noticed that if I updated a task on one of my devices (i.e., iPhone) while the others were in sleep mode, and then turned on my iPad, the task would already be updated, which was impressive.
Should the number of lists that one has matter? No, it shouldn't and it's challenging to determine if that was causing the sync issue OR if Apple did something within the past half day or so on their end (i.e., updated iCloud, at some level) to address the issue.
I'm not getting my hopes up just yet - as some of us experienced, including myself, when we did the Reset All Settings option, it didn't last too long. I'll continue to monitor over the next few days. Also, I'm likely not going to factory reset my iDevices until after (if need be) iOS 7.0.3 and 7.1 are released, within the next couple of weeks/months (as the rumour mill goes), in case this addresses the issue permanently.