Apache :: Blocking Bots And Spam Referrers?

If I know the IP range that I want to block the best option is to block it with IPTABLES. This works well when you want to block entire countries. But what happens when you want to block specific IPs rather than ranges? Is iptables still more effective than "deny from [IP]" in .htaccess? I read that you don't want iptables to grow too big as it slows performance, but I guess it is still more effective than having big .htaccess..?

When it comes to blocking spam bots or referrers, robots.txt is just a suggestion for bots, when I looked at my traffic logs I noticed that most bots don't even look at robots.txt file. As far as I understand the only option here is to use .htaccess

1. I am currently using this in my .htaccess:
SetEnvIfNoCase User-Agent *ahrefsbot* bad_bot=yes
SetEnvIfNoCase Referer fbdownloader.com spammer=yes
...
SetEnvIfNoCase Referer social-buttons.com spammer=yes
Order allow,deny
Allow from all
Deny from env=spammer
Deny from env=bad_bot

2. Apparently, there is another approach as per below:
# Deny domain access to spammers
RewriteEngine on
RewriteBase /
RewriteCond %{HTTP_USER_AGENT} queryseeker [OR]
RewriteCond %{HTTP_REFERER} ^(www.)?.*(-|.)?adult(-|.).*$ [OR]
...
RewriteCond %{HTTP_REFERER} ^(www.)?.*(-|.)?sex(-|.).*$
RewriteRule .* - [F,L]

Which approach is better #1 or #2? Any better alternative?

Finally, somebody suggested that you need to have both (as per example below). Is it true?

RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} ^rogerbot [OR]
RewriteCond %{HTTP_USER_AGENT} ^exabot [OR]
RewriteCond %{HTTP_USER_AGENT} ^MJ12bot [OR]

[Code] ....