One would assume that just because Magneton has more Speed and Bulk with Eviolite, that it is the better Steel trapper of the 2. Everyone does that. Well, I'm going to explain what separates Magnezone from Magneton. As you stated above, Adamant Choice Band Scizor must be taken to account here as a major threat. Well, being as CB Scizor has no Speed investment, it is good to say that Magnezone outspeeds this Scizor with only 44 EV investment in Speed, Modest Nature. This leaves the fact that Magnezone can outspeed and OHKO the Steel Bug because it has more Sp. Attack. This also means that the extra Speed Magneton carries is unneeded, and Magneton with have a harder time OHKOing things with that Average Sp. Attack. Another thing to consider is the Item spot. Magnezone carries the amazing Leftovers, and Air Balloon for nice immunities. Magneton needs an Eviolite to even take a hit, otherwise why use it over Magnezone?? You also mentioned Weather, at which Magnezone briefly likes, as well as Magneton, but Magnezone carries the higher Sp. Attack, making it a better launcher of Thunder and boosted HP Fires. I will provide Movesets as you wanted:
Rain
Magnezone @ Leftovers/Air Balloon
Trait: Magnet Pull
EVs: 152 HP / 180 SAtk / 176 Spd
Timid Nature (+Spd, - Atk)
- Substitute
- Thunder
- HP Water/ HP Ice
- Flash Cannon
This is my preferred variant for Rain. The EVs provide massive Bulk to tank hits like a boss, while still outspeed Skarmory and most Scizor variants. Substitute is used once you trapped a Steel Type. Thunder gets 100 acc, STAB. HP Water gets a boost in the Rain, while HP Ice covers threats such as Dragonite, Salamence, Latios etc. Flash Cannon is STAB, and nails Terrakion when needed.
Sand
Magnezone @ Choice Specs
Trait: Magnet Pull
EVs: 32 HP / 252 SAtk / 220 Spd
Modest Nature (+SAtk, - Atk)
- Volt Switch
- Thunderbolt
- HP Fire
- Flash Cannon
http://smogon.com/bw/Pokemon/magnezone That Will explain it better than me, but the EV Spread was taken from the SubAttack variant, as it seems better suited for a Specs Magnezone. Clear Skies would use the original SubAttack variant in the link, as it is best fitted for the situation of not having Weather