Offensive Snorlax and Lapras?

They are both relatively good in attacking as well. That being said, I never battle with any of them. Snorlax simply takes too long to kill a Pokemon and my Lapras has not the best attack move set, in which I prefer to choose Cloyster as an attacker.

Any Lapras with 2 ice type moves will destroy Dragonites. Especially one with frost breath/blizzard. Snorlax can be a bit underwhelming offensively. His best attribute attacking would probably be that he can take down 4-5 defenders on his own before fainting but he wouldn't kill them the quickest.

Snorlax is not the best attacker against anyone, but is alright against everyone, is the second best overall attacker. And Lapras is the best counter against the "stronger" pokemon in the meta (dragonite) that is very commom on gyms.

Lapras is awesome against Dragonite if it has Frost Breath / Blizzard.

Snorlax is awesome with Lick / Hyper Beam.

Snorlax is a bit slower because Lick is a low damage charge move without STAB but it charges up the Hyper Beam pretty quick and the HB is a real destroyer.

It depends a bit on your attacking style, but I love big charge moves - Solar Beam, Blizzard, Hyper Beam, Thunder, Earthquake, Hydro Pump, etc. even though they may not necessarily be the highest DPS. I find the load up and discharge really satisfying :-)