Octavia VRS - petrol versions sometimes have issued with the water pump housing leaking. Diesel versions have issues with the water pump itself failing, and older cars used around town are seeing some DPF related issues too.
Fundamentally solid cars. For the petrol versions, the specifications changed quite a lot during the model runs, summarised roughly as follows.
VRS 220 - basic pre-facelift model. 2.0 turbo with 220Bhp, same engine as the 2014 Golf GTI.
VRS 230 - 10bhp more, plus it got the VAQ differential which improves the handling no end.
VRS 245 - Now up to 245bhp with same engine as the Golf GTI Performance pack, these all got the 7 speed gearbox if you went for DSG (earlier models got the 6 speed), this is the facelift version for late 2017 with the split LED headlights, all 245s get the bigger 340mm front brakes, launch editions had lots of kit as standard, however over time the specification was worsened and things became optional extras again (heated and electric seats were once standard IIRC on the VRS245, but they became optional extras again after a while).
VRS 245 Challenge - I have one of these at the moment, an estate auto, its a run out special of the VRS245 with more standard kit (Dynamic Chassis Control suspension, Front and rear parking sensors, power fold mirrors, privacy glass and heated and electric powered front seats).
The diesel cars are all 184bhp 2.0 engines, throughout the model run, with no mechanical changes barring the front brakes (some had 312mm brakes, some had 340mm), so its easier to work out what you are getting mechically with the diesels.
I had a 2017MY Seat Leon Cupra 300 prior to getting my 2020MY VRS245 Challenge....and the cars were more different to drive than I expected. The Leon Cupra was obviously faster and also handled better, but since you're not looking at the Cupra, I'll try and stick to the differences that will be fundamental when comparing any Mk3 Leon/Mk3 Octavia. IMO the Octavia interior is a more staid design but the material quality and perceived solidness is much better than the Leon. The infotainment is much of a muchness, both my cars had versions of the VAG 8 inch sat nav/stereo which is brilliant IMO. Rear legroom and boot space obviously massively favours the Octavia. The Octavia is much quieter inside and generally a more refined, less sporty drive than the Leon. If you do a lot of motorway miles I suspect you'll enjoy the Octavia far more than the Leon.