How are you defining "Easy."
Let me preface this by saying that storage is, in fact, largely overrated for solar power. The vast majority of our energy needs occur during the daytime. Storage is really really nice to have, but is not entirely necessary unless you are producing much more than you need and don't want to waste it (see: Germany)
That said, let's talk "easy"
On a technical level, it's far easier to store electricity. Just need a battery or capacitor. If you want a more general form of solar energy as heat, then you just need a storage medium like water or oil or molten salt or whatever. Very easy and these storage mechanisms generally last a very long time with little maintenance if built properly.
Storing natural gas is a lot harder, again on a technical level. It's lighter than air and a fire/explosion hazard. It's moderately low energy density means it needs to be stored under pressure, so you need compressors and pumps to move it around. This means the very act of storing and transferring needs additional energy from secondary source - usually electricity.
If you define "easy" in terms of final stored density, then yes natural gas wins handily - especially if you liquefy it. But higher density storage requires more energy input, so your efficiency (energy invested in storing the fuel versus energy in the fuel itself) starts to drop.
If you define "easy" as recoverability, then it's a bit more complicated: batteries and capacitors give up their energy readily. Thermal storage requires an extra step to convert to electricity, if electricity is what you want... if you want heat then no conversion is necessary and again it's super easy to take out of storage. Natural gas can either be burned directly from storage if you just want some fire, or it could need converting into something else like mechanical power or electricity which are extra steps. You really need to define what you want to use the energy for to compare them, and they all have their strengths and weaknesses.
If you define "easy" in terms of infrastructure/investment required, that also gets a bit murky. Natural gas already has the benefit of decades and billions of dollars in storage and transport infrastructure development. Thermal energy has only modest transport infrastructure (district heating/municipal steam systems) and not much int he way of storage. Electricity has excellent transport infrastructure but storage is still in its infancy compared to natural gas... you can find the odd pumped hydro station or massive battery bank but most electricity storage is low energy/high power used for smoothing out spikes and sags.
With regard to your anecdote: Whomever designed it needs a kick in the balls, that's all. There is no sensible reason why a properly selected pump, for example, would fail every two years because of "too much heat." I'm a mechanical engineer with 16 years of HVAC design experience and I've never heard of that. Corrosion is not really a function of temperature - I suppose at the chemistry level it is, but a good and proper tank will be either coated or cathodically protected or both. There are tanks 50+ years old still in service because they were properly designed and installed. Sorry to hear of your troubles but it's just not the technology's fault.