When evaluating DNS servers, three key factors matter most:

1. Query Response Time (measured in milliseconds)
2. Cache Hit Ratio (percentage of cached responses)
3. Uptime/Reliability (measured in percentage)

Use dig or nslookup to test performance:

# Linux/macOS
dig example.com @8.8.8.8 | grep "Query time"
dig example.com @your.isp.dns | grep "Query time"

# Windows
nslookup example.com 8.8.8.8
nslookup example.com your.isp.dns

Windows PowerShell script to test multiple DNS servers:

$domains = "google.com","github.com","stackoverflow.com"
$dnsServers = @("8.8.8.8","8.8.4.4","your.isp.dns")

foreach ($domain in $domains) {
    foreach ($dns in $dnsServers) {
        Measure-Command { 
            Resolve-DnsName $domain -Server $dns -ErrorAction SilentlyContinue 
        } | Select-Object @{Name="Domain";Expression={$domain}},
                          @{Name="DNS Server";Expression={$dns}},
                          TotalMilliseconds
    }
}

Google's Anycast network provides global coverage, while ISP DNS might be physically closer but less optimized. Consider setting up a local caching resolver like dnsmasq:

# dnsmasq configuration example
server=8.8.8.8
server=8.8.4.4
cache-size=1000
local-ttl=300

Create a scoring system based on your needs:

def evaluate_dns(isp_dns, google_dns):
    weights = {
        'speed': 0.4,
        'reliability': 0.3,
        'privacy': 0.2,
        'localization': 0.1
    }
    
    isp_score = (isp_dns.speed * weights['speed'] + 
                isp_dns.reliability * weights['reliability'] +
                isp_dns.privacy * weights['privacy'] +
                isp_dns.localization * weights['localization'])
    
    google_score = (google_dns.speed * weights['speed'] + 
                   google_dns.reliability * weights['reliability'] +
                   google_dns.privacy * weights['privacy'] +
                   google_dns.localization * weights['localization'])
    
    return "ISP DNS" if isp_score > google_score else "Google DNS"

For privacy-conscious users wanting Google DNS performance:

# Using curl with DNS-over-HTTPS
curl --doh-url https://dns.google/dns-query \
     -H "accept: application/dns-json" \
     "https://dns.google/resolve?name=example.com&type=A"

When I first benchmarked DNS response times using dig, the results surprised me:

# Measuring response time for ISP DNS
dig @isp.dns.example.com google.com | grep "Query time"

# Measuring Google DNS (3 test runs)
for i in {1..3}; do dig @8.8.8.8 google.com | grep "Query time"; done

Google's 8.8.8.8 consistently showed 10-15ms faster response times than my ISP's DNS servers. But raw speed isn't the whole story.

Google's anycast network means you're not necessarily connecting to the nearest physical server. Tools like traceroute reveal the actual path:

traceroute 8.8.8.8
traceroute your.isp.dns.server

A DNS server geographically closer might outperform Google's in real-world usage despite benchmark differences.

For comprehensive testing, I recommend this bash script that evaluates multiple metrics:

#!/bin/bash
servers=("8.8.8.8" "8.8.4.4" "your.isp.dns.1" "your.isp.dns.2")
domains=("google.com" "github.com" "stackoverflow.com")

for server in "${servers[@]}"; do
  echo "Testing $server"
  for domain in "${domains[@]}"; do
    echo -n "$domain: "
    dig +stats +noall +answer @$server $domain | \
    awk '/Query time:/ {print $4 "ms"}'
  done
  echo "-----------------"
done

When configuring systems, consider these approaches:

Linux (systemd-resolved)

# Edit configuration
sudo nano /etc/systemd/resolved.conf

# Set DNS servers (example):
DNS=8.8.8.8 8.8.4.4
FallbackDNS=your.isp.dns.1 your.isp.dns.2

Windows PowerShell

# Set DNS servers
Set-DnsClientServerAddress -InterfaceIndex 12 -ServerAddresses ("8.8.8.8","8.8.4.4")

# Verify configuration
Get-DnsClientServerAddress

For maximum reliability, implement DNS fallback in your applications:

// Python example with fallback
import socket

def resolve_host(hostname):
    dns_servers = ['8.8.8.8', 'your.isp.dns.1']
    for server in dns_servers:
        try:
            resolver = dns.resolver.Resolver()
            resolver.nameservers = [server]
            return resolver.resolve(hostname)
        except:
            continue
    raise Exception("All DNS servers failed")

Modern operating systems implement DNS caching that can negate speed differences. Monitor cache hits:

# Linux
sudo systemd-resolve --statistics

# Windows
ipconfig /displaydns | find "Record Name"