In my experience (I serviced and repaired mowers and other arb machinery for best part of six years) a mower with an ally deck will out live one with a steel deck. Also consider Viking (made by Stihl) or Etisia with a plactic deck. I've seen plenty steel mowers scrapped that still have good engines. Cheap mowers tend to fall apart. The B&S Quantum and Sprint engine mowers are basic industry standard and go for decades. Biggest starting problem is stale petrol. The Sprint (with the carb mounted on top the petrol tank) has a pump diaphragm between the carb and tank and may need changing if left with stale fuel in the tank or every few years depending on use. There is a correct procedure that needs to be followed when fitting this pump or the engine will hunt or not start.
Avoid anything with a Tecumseh engine. Engines are prone to falling apart from vibration, are a pain to self service and repair in terms of strip down and rebuild... They are pretty shit. Some of the smaller Honda engines (GCV models) have plastic cambelts. I have known these to jump. You won't smash valves up but they are a pain to re-time.
Mower wise depends on budget and how big your lawn is. Do you want stripes, width of cut etc?... Do want a hover? If you do get a steel deck clean the crap from the underneath before storing away. Masport and Honda branded mowers are some of the best steel deck mowers in terms of lasting but Honda are mostly good solid plastic or ally decks. I know lots of contractors that use Masport, Rover, Hayter and Lawnflite Pro. They are totally abused but the ones with the cheaper service and repair bills are the ones with the Masport and the Rover. Masports and Rovers have swing tip blades to stop damage to the crankshafts.
A cylinder mower will give a better cut than a rotary mower.
With Husqvarna, yes you are paying for the name but when I was in the workshop they rarely came in as breakdowns.
Hayter used to be very robust but are now over engineered. Some newer models have ally top deck with shit loads of plastic underneath. This will be reflected in your service costs when smashed plastic parts need replacing.
Not mentioning your cheep Argos, Tesco budget mower... too many to mention but remember you get what you pay for. If you want one that will last here's a few makes.
Briggs and Stratton Quantum Engine on...
Masport
Rover
Viking (Stihl)
Etisia
Honda with GXV, HR, HRX engine.
Briggs and Stratton Quantum Engine on...
anything that doesn't look like it's made of chocolate. If it feels cheep and flexible in build it is chocolate and will brake in a few seasons.
Do not buy anything with a Tecumseh engine and stay well away from the Lawnflight Pro 553HRS