Giving nothing is always best if you can - have a worm egg count done (by your vets or Westgate) and then worm according to the results. You could check for tapeworms too with a saliva test if you haven't in the past. And think about whether bots are an issue in your area. The results of these will tell you what to use if you do need to worm. Wormer names are not particularly useful because there are several brands using the same active ingredient, so go by ingredients:
benzimidazole = lots of resistance, avoid
pyrantel = redworms, double dose for tapeworms
ivermectin = redworms, bots
praziquantel = tapeworms
moxidectin = redworms (drug is stored in body fat, I'm not keen on it)
I’ve just done a count, and westgate have recommended those that have come back with medium or high, to be done with an ivermectin wormer. I’ve ordered animec and it’s cost me including delivery £5 each
Just suggest never use Pramox. I worm counted in the spring and they needed done so the lady in the shop recommended this for what they needed. Both horses were unhappy after it, one just looked depressed for days, the other tried to bronc me off when I got on her which is extremely unlike her. Left her another week and she was fine again. Awful stuff.