best way to create test data

public class CreateTestData {
    List<Account> acctList = new List<Account>();
    List<Opportunity> oppList = new List<Opportunity>();
    List<Client_Plan__c> clientList = new List<Client_Plan__c>();
    List<Client_Plan_Product__c> clientProdList = new List<Client_Plan_Product__c>();
    List<Tasting__c> tasteList = new List<Tasting__c>();
    List<Tasting_Product__c> tasteProdList = new List<Tasting_Product__c>();
    public List<Account> CreateAccount(String testName, Integer count) {
        for (Integer i = 0; i < count; i++) {
            Account acct = new Account(name = (testName + i) );
            acctList.add(acct);
        }
        insert(acctList);
        return acctList;
    }
    public list<Opportunity> CreateOpportunity(String testName, Integer count) {
        if(acctList==NULL) {
            CreateAccount(testName, count);
        }
        for (Account acct :acctList) {
            for(Integer i = 0; i <count; i++) {
                Opportunity opp = new Opportunity(Name = (testName+count), AccountId = acct.id);
                oppList.add(opp);
            }
        }
        insert(oppList);
        return oppList;
    }
    public list<Client_Plan__c> CreateClient(String testName, Integer count) {
            if(acctList==NULL) {
            CreateAccount(testName, count);
        }
        for(Integer i = 0; i <count; i++) {
            Client_Plan__c plan = new Client_Plan__c(Name = (testName+count), Account__c = acctList[i].id);
            ClientList.add(plan);
        }
        insert(ClientList);
        return (ClientList);
    }
}