The problems with relays are well known and understood. Choosing a suitable relay and protection circuit is much easier than using a triac (in my opinion anyway). If we're talking about a significant amount of current, you'll need a heatsink on the triac which normally negates any size advantage. My background is in power control - more specifically lighting control. So, I've used a few triacs in my time and a few relays. I'm not saying triacs are inherently bad, they are fairly reliable but they need more care and feeding compared to a humble relay. Relays also have a higher demonstrable reliability.

Put it this way, get a 10A relay - garden variety. Feed it 230VAC through a standard C curve din rail 10A circuit breaker into a short circuit. See how many times you can activate the relay before it fails. Now try the same with a 16A triac (40A if you like) - it will most likely fail the first time and generally will not survive past 3 times. Also, with the triac you normally require an optocoupler - these too have issues of wearout. Also look at the cost implications - a 10A name brand relay costs me about AUD$5 in small quantities with a led indicator. An equivalent SSR (solid state relay) is at least AUD$20.

Ask yourself "what is safer"