Which approach would you be most open to if a sales rep was to engage you for the first time?

Trying to contact me is a waste of time. I keep abreast of the industry and technology. When I see something of interest I will reach out. Just be sure you are at industry events, both National and Local.

Send me a high value piece of content tied to a need I have

Most newer BDR's fail miserably at cold calls and cold emails. Whenever possible - connecting at industry events or setting up an offsite, low-stakes discussion (coffee) works best in my opinion. 

The goal of the cold call/email is important - I would most likely use both of these to try and set up face to face time.

I know that 'sales' is a difficult job and someone has to do it, but I wish sales team would remember that their cold email (or call, or LInkedIn msg) is not going to be the only one I receive today, it is one of many, all of which tell me they have the best product for me (without even knowing my needs) and all of whom 'just want to jump on a quick call' or to 'pencil in a chat tomorrow'.  

Like I say, Sales is difficult, but as others have said in the comments below, when I want to purchase a product I will do my research and contact the relevant vendors, hopefully with a referral for a particular product.  And, not forgetting that any purchases have to go via a well defined procurement process anyhow.

So, I hate to say it but cold calls and emails go unanswered, otherwise it would be a full time job responding.

The chances of me hearing you out if you've called me unsolicited is approaching zero for every second the call goes on

Same with social media, if a salesperson connects and then tries to sell to me before any rapport is built, blocked and message reported for the spam it is

If you send an email, and it has a value proposition relevant to me or the business, I'll hear you out for 30 mins on a scheduled call