1. What's the end game for this comic? Is it one you're going to keep for your personal collection? Are you getting it graded to sell it?
A. If you're getting it for your personal collection go with the company you prefer. Realize that the two big third-party graders, CGC & CBCS, will have long turnaround times. You'll have to factor in that if your book is of high value that the grading will cost more and not just the standard rate. There are a few downsides to CGC as of lately as there have been a few instances of label errors and newton rings. If you're not familiar with them a quick Google search will give you all you need to know about them. CBCS has recently upgraded their cases which a majority of collectors have praised. Also they the only company that will verify a signature and assign it a red label. This is what I have heard might be phased out, so I'd work on getting that done sooner than later.
Now some collectors don't care about grades and will just send their books as is. I like to work the odds in my favor to get my book pressed/cleaned prior to submission. If you're unfamiliar there are several hobbyist that have picked up the craft/trade of cleaning and pressing comics to improve their appearance and move the book up to a higher grade potentially.
B. If you're getting something graded to sell, there are a few things to keep in mind. First thing is to figure out if it's worth the price of grading. You'll have to search through a few price guides to figure out values. A great tool to use is eBay sold listings of the particular comic book to find a real world value of what someone has paid for it. Then you have to determine which grading company to use. Now CGC is going to take a little bit longer depending on if you pay for fast track option. But several people have experienced delays all around, including myself. If you go through CBCS, values can go down by 10-30% in contrast to CGC. Lastly don't forget to factor in shipping so that you can make sure you profit on your submission.
2. If you're submitting with the purpose of selling the graded books, ask yourself are they in demand? There are several examples of books that are graded that are just filler books or books that don't have a market. Many times you can come across a hot book and submit for grading to find that when they do come back the steam has let off and the book isn't in demand as it was prior. Unless you know your customer base and they're sure to buy it's a risk to consider.
Don't forget to factor in shipping of your graded book after it sells as well as supplies and the cost associated with using whatever selling platform you'll be using. Plus, often times you're won't get the exact price that you'll be asking. So it's a good practice to run the numbers a number of times to make sure it makes sense for your situation.
Also be prepared to be let down that some times your comic won't get graded at the particular higher grade you're wanting. Just recently a comic I sent in graded several grades lower than expected from myself and the presser I was using at the time. This is just another factor to consider in your decision making process.
My advice is to do thorough research with several different price points to make sure you profit. A safe bet is always a high grade key book or a highly collected title like the Amazing Spider-Man. If the book is going in to your collection are you going to display it or keep it in a box? There are several different options for storage and display but that might factor in to your decision that you may have neglected to think about. And as always, if you need help feel free to reach out with questions.