Take my adivce I go to the Smogon In-Game Tier list everyday.
Excadrill
Excadrill as a awesome defensive typing, only beat by Fighting, Water and Ground. It's Steel typing let's it be Immune to Poison which is helpful. Excadrill has awesome Base HP while pretty decent Defensive Bulk. Excadrill has the inferior ability, both only activating when Sand Storm is up. As a Drillbur, it isn't much useful until Lvl 19 when it gets Dig. With Dig you have a 80BP STAB move you can take advantage with because Drillbur has 85 Base Atk. Then it will get a Set-Up Move, Hone Claws, that increases your Acc. and Atk by one Stage. The next noticable move is Rock Slide at Lvl 29, and with one Hone Claws it will be a
112BP move with more then 100%. Then it evolves into Excadrill at Level 31 with amazing Stats (110/135/ 60/ 50/ 65/ 88). Then gets Earthquake at Level 36, oh and don't forget about Excadrill's Def. Typing + Bulk! With that you can easily get a Hone Claws in and make that 100BP EQ (150 with STAB) into a 150BP move (225 with STAB) The last noticable move is Swords Dance at Level 42. Sandstorm is pretty decent, as it can be a psuedo Agility with Sand Rush.
Potentional Set: Rock Slide, Earthquake, Metal Claws/Sandstorm, Swords Dance
Crookodile
Crookodile has the superior ability of the two, and the amazing In-Game ability Moxie. Every Crookodile should have Moxie on it, because it will allow you to get a +1 Atk. boost for every Pokemon you defeat, wow! As a Sandile, it's only noticable attack is Assurance, but since Sandile and it's evolution's have pretty decent Speed, you will rarely get the 150BP (with STAB) Assurance. You an get TM 28 (Dig) from Route 4, so it can use that as a main STAB move. It gets Crunch at Level 28, right before evolution. Once it evolves into Krokorok, it gets nothing good by Level up until it evolves at Level 40. As a Crookodile, it gets Earthquake at Level 54 and Outrage at Level 60. Crookodile has pretty good Base Stats (95/117/ 70/ 65/ 70/ 92) with a Higher Def, Sp.Def and Speed as Excadrill
Tl;dr: Excadrill is better early/mid game. While Crookodile is better after game.