Well, what's the difference?
Proofreaders analyse your manuscript for spelling, punctuation, grammar and syntax mistakes.
Copy-editors address all those errors, but also check your facts (very important for non-fiction) and consistency.
Line-editors address all of the above, but also your writing style, voice, and your story as a whole.
The other obvious concern is cost. Proofreaders usually charge between £5-8 per 1,000 words (I charge £4), copy-editors between £8-11 and line-editors from £12+. There are a couple of reasons for this. Line-editing takes longer than copy-editing, which takes longer than proofreading, but they also requires a different set of skills.
So which type of editor is right for you?
If you are thinking of submitting to literary agents (and I would absolutely recommend you do this before considering self-publishing) I do NOT think you need to pay for a line edit.
Because if you do land an agent they will then line edit your manuscript. And if they manage to sell your book to a publisher, the publishing house will then line edit it again.
Every editor has their preferred style. One editor might like your voice, or a certain character, or a plot twist, whilst another might not. One editor might think your story needs more pace, another might not.
The same with readers. Some readers will like your book. Some will not, no matter what you do to it. If you change it to suit a certain editor, the outcome stays the same: some readers will like your book, and some will not.
Changing any aspect of your story or your style to suit a specific editor is only worth doing if you know it will improve your chances of success.
If the line-editor combing through your manuscript is your agent, and you've done your research and you know they are successful in selling books to publishers, you can be confident they will add value. Also, your agent will do this for free. Your agent will know which publishers they intend to pitch to and will know (should know) what kind of stories and styles they buy.
If you do have the money to pay for a line edit and think that's the way to go, you want to find a line-editor who has a good track record helping authors get picked up by agents. Don't just look for qualifications. Experience is what matters.
Your writing style and your voice need to come from you. They cannot be outsourced. But how do you find your voice?
Write a lot. Write a lot and read a lot. It will come. There is no substitute for practise.
So. You've decided against a line edit. Why would you want a proofread?
It doesn't seem to matter how often you read through your manuscript, writers always seem to miss something. Maybe it's the wood for the trees.
Putting your finished manuscript aside for a few weeks before coming back to it does seem to help. But sometimes you need someone else's fresh eyes. I can catch those grammar slips we all miss from time to time. Point out the odd awkward phrase or that paragraph that doesn't quite make sense.
I won't tell you if I think a character is weak, or the piece needs restructuring, or it needs more pace. Why? Because that's all subjective, and I don't want to force my preferences on your manuscript. Other readers have different preferences.
So I won't tell you to change your story. But I will help you improve your writing. Grammar is not subjective. Agents will reject anything with poor grammar - don't let it spoil your chances! If you think you have a great book but know grammar is not your strong point, drop me an email. I can help.
Cost of my proofreading service is £4 per 1,000 words. I also offer a fiction submission package for £40 (cover letter, synopsis and first 10,000 words). More information here.