Each deck has two reprint commanders, with one ranking in the top 25 and one just outside the top 100, so it really comes down to personal preference
"[Type]cycling [cost]" means "[Cost], Discard this card: Search your library for a [type] card, reveal it, put it into your hand, then shuffle." This type is usually a subtype (as in "Mountaincycling") but can be any card type, subtype, supertype, or combination thereof (as in "basic landcycling")
Think of the possibilities
While some of these cards, individually, will only cost you a few cents, there are those out there that may require you to break open any spare piggy banks you have lying around
The sheer card advantage Tiamat creates on ETB is well worth it on its own, but its also one of many Food Chain combo enablers that you can put in the command zone