If AT&T Fiber is available at your address, it’s almost always the better pick: faster (300 Mb/s → 5 Gb/s) and symmetrical speeds, lower latency, no data caps, no promo-price jump and the highest customer-satisfaction score in the industry.
If you can only get AT&T’s older DSL/IPBB service, Spectrum wins: its cable network delivers 100 Mb/s → 1 Gb/s down (10 – 35 Mb/s up) with no contracts or data caps and wider U.S. coverage.