Depends what sort of budget you have cause there are thousands of options depending on the amount of money you want to spend.
From experience i would recommend the following
£10-£20 - Collinite 476s, PoorBoys Natty Blue, Chemical Guys xxx, Megs no.16
£20-£30 - DoDo Juice Hard Candy
£30-£40 - DoDo Juice Rubbish Boys Juiced Edition, DoDo Juice Purple Haze Pro
Over that i have tried DoDo Juice's DetailingWorld Double Wax (2 seperate waxes that you layer over each other). That retails at around £70 for the full size pots. Then there is DoDo Juice Supernatural wax which retails for around £90, this is their top end wax and is pretty special.
You can also get any of the DoDo Juice waxes in panel pot size (30ml) which doesnt sound like a lot but will give you around 5-6 layers on a Leon or
Ibiza is applied properly.
As i said, there are thousands of waxes and sealants out there, the above are what i have used and would recommend to anyone. Generally the more expensive waxes offer better durability and add a little something to the finish but the ones in the sub £20 bracket are very good products for the money and shouldnt be excluded.
In all cases the finish that the wax gives is only as good as the prep... having a finish pre wax which isnt right will decrease the finish of the wax and cause disappointment. If you have a good finish the wax will enhance it.
HTH, Nige