Card Grading Companies and why grade cards
Generally people grade cards because it could make the price go up. Cards that I've seen that make the value of the card rise is cards that are normally sought after. For example the 1993 SP RC Derek Jeter or the 1994 SP RC Alex Rodriguez. A problem with grading cards is that if your card gets a low grade it might make the value of the card go down. Just look at what ungraded 93 sp rc Derek Jeter's are selling for vs. what low graded Jeter's are selling for. Generally the ungraded cards sell for more from what I've seen. Now about everybody else.
BGS (Beckett Grading Services)
Beckett Grading Services is my favorite grading service because they have an internal sleeve. This prevents the card from moving in the holder unlike some of my cards from other graders. BGS is known among collector's for being a tougher grader. They're also slightly cheaper than PSA last time I checked. You can check for yourself to make sure this statement is still true at the time you're reading this.
PSA (Professional Sports Authenticator)
PSA is a good service because they've been around for a while and their cards sell. Some collector's say that they prefer PSA for older cards but I'm not sure why that is. I graded a 94 SP RC with them and sold it for about $95 and this was about four years ago.
Other Grading Companies
Generally other grading companies just don't sell. Some people seem to like SGC (Sports Card Gurantee) I've never graded with them however there prices aren't too different from PSA or BGS so I would prefer to grade with them. Currently when I checked they did have a nice special $5/modern card.
Grade My Cards (Grademycards.com)
I like that their holders are similar in quality to PSA. I still think PSA holders are better however, their prices are cheap and turnaround time is fast. You can grade a card with them for $1.99 with just a number grade and $2.99 with full detail grading. For $0.99 you can get your card encapsulated but not graded. They recently added an extra charge of $1 (I noticed this in 09/08) for autographed cards. That is my favorite feature with them because I can get autographed cards authenticated and then just have them encapsulated. I also like to send them cards I don't want to sell because their holders are similar to PSA, although I stress that PSA is better. Some cards in their holders move around too much. I've noticed that their cards don't sell for too much on eBay however I tested them out and they don't just give out tens. I purposely sent them damaged cards which came with lower grades then the good cards I sent them. They're my favorite graders because they're inexpensive. Unfortunately I wouldn't send them anything I would want to sell for a lot of money because people simply prefer BGS or PSA.
So I tired these guys out because they're even cheaper than grademycards.com Their holders are better than grademycards.com in my opinon because they're a little bit tougher. I dropped a grademycards holder and it seemed to chip too easily. I must admit I've never dropped a BGS/PSA/GMA holder. Anyway I was not happy with their grading service. I sent them a card with a messed up corner and it got a 10. One of my cards was an autograph card and the label said Jersey. If you want to just get your cards placed in holders and you don't care about the grade then I would go with them. If you care about the grade don't go with them.
I tested out GMA and GradeMyCards and I've noticed that if you want to sell graded cards PSA and BGS are the way to go. I personally prefer the BGS holder. However they're more expensive so in the future I think I'm just going with the encapsulation only service of GradeMyCards. If GMA were to come out with a similar service I would go with GMA (as of 09/14/08) GMA doesn't offer and encapsulation only service. If I wanted to sell a modern card I would go with BGS. For older cards I would go with PSA only because I've read other guides saying that PSA is better with older cards. I hope my experimenting of these two smaller companies has helped you.
These statements are simply my opinion and nothing more. I'm not affiliated with or related to anyone who is affiliated or even friends with anybody affiliated to any card grading companies. I"m just a collector posting my opinion based on my experience. Yours may vary so don't use my opinions to make any investments :0). If you are a member of one of the companies I mentioned. These are only my opinions! When I have time I'll add some pictures to this guide to make it better. If you find it helpful please vote that it was helpful.