Are SD or CompactFlash cards inherently more reliable for still photography?

In general the top tier Compact Flash cards available to the typical consumer via retail channels when compared to the top tier Secure Digital cards available to the typical consumer via retail channels are:

• More rigid and less susceptible to damage from flexing
• Rated for more extreme environmental conditions (higher altitude, lower temperature, etc.)
• Have faster write speeds (although this gap has been narrowing recently), even when read speeds are the same or very similar
• More expensive

Additionally, CF cards use the standard IDE protocol to communicate with other devices. SD cards use their own protocol that has been modified/extended several times (e.g. SD → SDHC → SDXC → UHS → SDIO). Device compatibility with SD cards newer than the device can be an issue. Newer, faster CF cards tend to be more backwards compatible with older devices, albeit at the older device's speed rating.

SD cards only have enough connectors to move between one bit (original SD standard) and 8 bits/one byte at a time (only the fastest, most advanced UHS-I or higher cards). CF cards have 50 connector pins and enable multi byte parallel write or read at the same time. Your camera must support multiple port parallel write to take advantage of this difference.

On the other hand, the pins on devices that use CF cards can be bent while the connection between SD cards and their compatible devices are less susceptible to damage from card insertion and removal.

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Appendix (probably obsolete by the time it is typed) Current fastest transfer rates as of August 24, 2015 as specified and available on amazon.com

SD cards: SanDisk-Extreme-UHS-I-Memory-SDSDXPA-032G-AFFP Capacity: 32GB Protocol:SDHC I, Class 10, U3 Speed: Up to 95MB/s Cost: $29.95

CF Cards: SanDisk-Extreme-CompactFlash-Memory-SDCFXPS-032G-X46 Capacity: 32GB Protocol: UDMA-7, VPG 65 Speed: Up to 160MB/s Cost: $59.95