Sometimes the game works well sometimes it is very laggy. From my own investigation this is due to many US ISPs including Comcast route their traffic to Montreal, Canada with Level3. The Level3 hop is often overloaded more often at night introducing a lot of lag into Final Fantasy XIV.

The following hops, both introduce a lot of latency into FFXIV.
ae-10-10.car2.Montreal2.Level3.net
ORMUCO-COMM.car2.Montreal2.Level3.net

The only way this is really going to be fixed for a lot of Comcast and Verizon customers is if you move the servers out of Canada and set up a data center somewhere in the United States. It is the level3 bottleneck in Canada that makes the game unplayable some of the time. The latency spikes to over 300+ ms at times on all the level3 hops in Canada.

Name of your Internet Service Provider (ISP): Comcast
Ticket or reference number from your ISP: NA
State/Country: OR, USA
Date/Time: Intermittently
Frequency: Intermittently
Content: Everything
Which in-game World were you playing on when the issue occurred?: Sargatanas