The combination pills, Bravecto and Nexguard, are being blamed by pet owners and some vets for horrible illness in some dogs. You cannot get it out of the dog for mONTHS if the dog reacts badly to Bravecto. A friend's Lab experienced vomiting after nexguard. Interceptor or Heartgard Plus for heartworm and worms and Frontline Plus for fleas and ticks may be the safest chemical treatments. I do not give them on the same day but about a week apart.
I have also used Revolution to protect my dogs when the area foxes had mange. It is a heartworm and flea med, and removes roundworms. It only works on some ticks.
Check manufacturers' websites or your vet for rebates or coupons.