This may make your decision harder, but here goes:
Most folks instinctively rate the Simmerlight (or similar pressurized white gas stoves) as superior for heavy duty uses such as snow melting and, as L. Savage says, welding, thawing pipes, etc.
Caviat: Snow melting requires flame control. You have to be able to keep the flame down (close to simmer) to avoid burning the pot out. A stove that won't simmer is out, regardless of its heat output.
Just because everyone says it don't mean it's true.
A cannister stove is about twice as efficient as the Simmerlight per ounce of fuel, and WAY better for base weight. All things being equal, it is usually better to go with what you know.
However, the care and feeding of cannister stoves is trickier in cold weather. IF you keep the cannister reasonably warm, a cannister stove will work until temps hit the teens. (Adepts may be able to make them work in colder conditions. I wouldn't know.)
That's a big if. You have to use tricks such as sleeping with the can, parking it inside your jacket for the last mile or two before you use it, using an insulated base and using a proper wind screen. See other discussions on the BPL site for information on wind screens for cannister stoves. You have to avoid overheating the cannister - which is easy to do with a poorly designed or improperly deployed windscreen.
Don't be shy about trying alcohol. The Trangia sytem is the original snow-melting machine for alpine mountaineers since the 1920s. I'm talking about the Trangia system: an alcohol burner used with the Trangia pot/lid/lifter/support/windscreen set (about $70). It will simmer, and it will ALWAYS work in awful conditions. That's what it's for - melting snow then the going is rough.
With one pot, the Trangia weighs 23 ounces (with the pot lid). That is an ounce lighter than the Simmerlight (8.5 oz. burner and pump + 2.7 oz. for the eleven-oz. fuel bottle) when you count the things the Trangia comes with and the Simmerlight does not: a not-too-light, snow-melting pot, lid (.5 oz foil although I did not subtract the Trangia lid), pot lifter (1.25 oz MSR), windscreens (1.5 oz), stove base (Trillium 2.25 oz) and repair kit (2oz)for a total of 26+ oz. The weight adds up like the cost - $160-170 for the Simmerlight stove and all its accoutrements, not counting the pot.
NOTE: Snow melting is hard on pots. Super lightweight pots require super care, good technique and some luck.
Of course, you need more weight in alcohol to melt the same amount of snow.
If you are consistently below 25F pure methanol lights better than ethanol in any alcohol burner. The original Trangia directions called for methanol at altitude and in snow. They knew what they were talking about.
In subfreezing weather, I use a little twist of fiberglass as a wick in the well to facilitate lighting the Trangia or any other open-well alcohol burner.