ATM my (evolved) Dweble has both of those moves because I can't choose between them, but I want to delete one of them for rock polish or possible stealth rock (works wonders against gym leader and bosses, against the electric gym I defeated an emolga by just stealth rock attacks cos it kept volt switching xD).
Rock Slide: 90 accuracy 75 power 10 pp May cause flinching
Rock Blast: 90 accuracy 25 power (per blast) 10 pp Hits 2-5 times ----------------------------
The flinch from rock slide is really nice, but rock blast has the possibility to hit 4 or 5 times causing a ton of damage (with STAB). Right now I think I prefer Rock Blast cos I think it's cooler :)
Can someone help though to say which is better? cheers.
Also, My evolved Dwebble (forgot it's name lol) also has X-scissor (found a TM) and Slash. Hopefully stealth rock or rock polish will replace either rock blast or rock slide.