Hi, I'm told that too long a title is not search engine friendly, but in other SEO tips, they suggest me to add my company name or site name to the title, what should I do? Add or not add? Thanks
Its very subjective.. It depends on the competition of the keyword, prominence,etc.,etc., So Blindly to say "Dont add" . Just keep your title very targeted and highly prominent.
Titles should neither be too short (vasting potential) nor too long (ugly and confusing for potential visitors). If you add your company/site name, do it on the end of the title, especially if it's a long company/site name. As Jawahar said, there isn't a general rule or recommendation and it won't make a significant difference as long as your site/company name isn't a well known brand.
Now days major search engine specially Google gives specially attraction to keywords added under page Title. So added your targeted keywords there. Don't waste your Title length with your website URL of company name. If its necessary to add then add it on Meta Title tag. Your Title tag length will not be exceed to 3-4 keywords or 70 character.
if your keyword is appropriate, unique and effective you can add the title but it should be short and go with the site