The avid was marginally better.
Thats because they are essentially the same aircraft.One of the partners that designed the kitfox left to set up his own company Avid. ( or vice versa .I can't remember)
As an aside he also produced the catalina flying boat and a huge twin that was used as a flying hotel by some famous explorer .
Because he took all the experiance with him, the mk1 avid was essentually a mk 2 kitfox, so it was always half a model in front.
As the models progressed they certainly got better.
I had a very early Mk1 kitfox and soon learned that a few minor mods ( like gap seals on the rudder ) really improved it.
The kitfoxes and avids were really advanced microlights dressed up as gp A aircraft and got a bad rep when group a pilots bought them by the dozen as a means of cheap flying.
They knew nothing about flying low inertia aircraft and so many of them crashed that you couldn't get insurance on them .
Meanwhile, the people that had the skill to fly them ( microlight pilots) were denied the chance because they were group A.
Things have moved on a bit now and their faults are better known and understood and they now have quite a following. The early ones give some of the cheapest flying available and you need to be conversant with two stroke engines and willing to give them the attention they need to be relaible. If you love tinkering and enjoy taking engines apart it could be ideal. If you don't know the difference between a crankshaft and a camshaft then its not for you.
The later models with the rotax 4 strokes are much closer to "normal " light aircraft.
There are better aircraft out there that are more robust and possibly take less looking after for much the same purchace price, eg aeronca chief & champ, piper vagabond, or if you like wood the choice is even greater.
None of these have wing fold though and hangaredge will cost much more.
If you are unlucky enough to need an engine a new continetal will cost more than a complete kitfox. A rotax 582 can be rebuilt for £700.
Flown on a nice day a kitfox can be real fun, If you are happy to pick when you fly and accept some foibles the kitfox can give a lot of fun for little money. if you have a little more money available a Champ is a much better aircraft.
You get what you pay for there's no free lunches in flying but plenty of £100 ones!