Is RG-6 coax cable better than RG-59 ?

In most TV cabling applications, RG-6 is better than RG-59.

Coaxial cables use RG (radio-guide) ratings to distinguish between the different cable standards. The numbers are randomly assigned without a specific order. RG-59 is an older standard that was designed for lower frequencies, RG-6 is a newer standard designed to incur lower loss over higher frequencies.

RG-6 cable
RG-6 is generally a much better choice for anything over 50MHz, such as, Cable TV, Satellite, Broadband internet, FM and VHF/UHF HDTV antennas. RG-6 was designed to be more effective with higher Gigahertz frequencies, and incurs less singal loss compared to RG-59.

Typical RG-6 Signal Loss per 100 ft:
50 MHz: 1.5 dB
100 MHz: 2.0 dB
400 MHz: 4.3 dB
900 MHz: 6.8 dB
1000 MHz: 7.0 dB

RG-59 cable
RG-59 is generally better for frequencies lower than 50 MHz, like CCTV systems. It is an older standard cable that was used for TV connections, however, it has a smaller conductor than RG-6, and its shielding is not well suited to keep higher Gigahertz frequencies inside the conductor very well.

Typical RG-59 Signal Loss per 100 ft:
50 MHz: 2.4 dB
100 MHz: 3.4 dB
400 MHz: 7.0 dB
900 MHz: 11.1 dB
1000 MHz: 12.0 dB

Notes:
For all intents and purposes RG-6 and RG-6/U are the same.
Outdoor rated cables have a "PE" jacket instead PVC to make them more resistant to cold weather, moisture, chemicals, abrasion, etc. They also have a special gel-like substance in the jacket to block moisture from corroding the conductor.