They have their pros/cons. Silvia is heavier - which can be a pro - less likely to move on your bench, or a con depending on whether you want to take your machine on holidays (hard to beat the Lelit for a weekend traveller* :)
Lelit body is all stainless steel (Silvia is powdercoated steel and can rust under the drip tray area) but the steel on the Silvia is so thick its unlikely to fall apart in a hurry!
Lelit has a bigger drip tray - a backflush with chemical will generally (over)fill a Silvia drip tray.
Lelit has a water tank level display so youre less likely to run out of water mid-shot. But Silvia is easier to fill - lift the lid and fill; Lelit - lift lid, take hoses out of tank, lift tank out and fill. But you can move the Lelit with water in the tank without a spill.
Both can be accessorised (naked pf, fitted tampers)
Both can make great coffee, but the standard baskets in the Lelit are deeper than the Silvia and in our experience tend to make it easier to get good extractions than the shallower baskets in the Silvia. However you can get deeper baskets for the Silvia.
The Silvia steam valve seals better (less likely to drip) due to the use of a soft rubber seal, but this seal will need to be replaced at regular intervals - especially if there is an "overtightener" in the house.
The Silvia has a longer steam arm and balljoint so its easier to position, but if your technique is good, they will both make excellent silky milk and it is just as easy on either machine.
edit: And the Lelit heats up faster.
Pick the one that ticks more boxes on your wish list and youll pick a winner.