I perfeer the Garmin GPS. Here is why.
No line if sight restrictions no accidentally getting the yardage to a tree instead of the flag stick,and when your out of position you can instantly see what the yardage is to put you back in play to any yardage you want for your next shot. Try that with a Lazer!

I have a watch GPS and a laser without a pin reader or elevation change estimate. I'm relying more on the watch. If the course uses different color flags for pin locations, front and back is all I really need. If the distance to the pin from the edge is critical due to a bunker and the pin on the same side as my ball, I'll laser the pin to see how much green I have to work with. The watch is just faster than finding a sprinkler head that may be missing the distance or 30 yards from my ball. My other use of a laser is to estimate a distance to lay up to from an obstructed shot My depth perception isn't very good so I don't want to short myself or go through the fairway on the other side.

With all due respect, Todd, with the exception of your line of sight point, a rangefinder can do everything you mention and a whole lot more that a GPS cannot do.

Today's high quality rangefinder's know whether they are shooting a pin or the trees behind the pin with no question. And they let you know with a signal when you have the pin. They are also more accurate than a GPS. And best of all, they will tell you exactly how far it is to any point you can see, be it the back of a bunker, a limb hanging over the fairway, a cart with golfer's in the group ahead, or any other point which may be helpful in making your next shot.

And, with 5/1, 6/1, or even 7/1 magnification, they can give you a much better idea of the green complex so you know how much room there is between bunkers and green surface. It's like carrying a pair of binoculars which allows for better assessment of the situation at hand. A GPS won't give you a good visual of the topography the way a pair of binoculars or a rangefinder will.

A GPS will not tell you what distance various targets out on a range are either, but that's another argument.

I personally used a Garmin GPS for years. And I actually still do since the carts we have at my home course have it onboard. It is helpful and convenient. But in my opinion, nothing beats a good quality rangefinder. I can't tell you how many times the GPS has been off by 10 or 15 yards to the pin, which it can only guesstimate. That's a club difference. Sure it will give you front, center and back which can certainly be helpful (and I use it for that info regularly), but it doesn't really know exactly how far the pin is from the tee on a par 3 or from where you are hitting your approach. The GPS units on our carts guess at yardage to the pin based on what quadrant the pin location is for the day. A rangefinder does not guesstimate anything.

So ideally, to reply to the initial poster's question, I would definitely consider a rangefinder, IN ADDITION TO your GPS unit, for maximum advantage. But if I could only use one, a Bushnell Tour V4, Pro X2, or Tour X would be at the top of my list.
Each offers slope readings, something GPS can not give you. Though the slope option can not be used within the rules for tournament play, it is a very helpful tool for general rounds of golf, particularly on courses on which you play tournaments. And slope can be turned off for legal, within the rules play.

One last point, to address the concern about line of sight. True, a rangefinder can not see through hills, but for the few instances that a situation like that arises, I just walk or drive my cart to the peak of the ridge, shoot my target, then either walk off the yardage back to my ball, or if I left the cart at my ball, just shoot the cart distance from the ridge, then add the two yardages together. Simple and easy. This method also allows for a good visual of the green complex. Looking at my GPS in a blind situation such as this, without actually looking over the hill for a true visual, doesn't really tell me much other than how far the center, back and front of the green are from me. Directional reference is lost without line of sight.

Okay, I'll step down off my bully pulpit now and let someone else offer their opinion.

I use both a GPS and Laser. My laser is used 98% of the time because it accurate + or _ 18 inches. It also gives me two yardages. Line of sight and true golf range. In other words if you have a uphill green the line of sight may be 150 yards but the true golf range will be 161 yards as an example. I use the GPS to determine the yardage when the pin is out of sight or I want to know what I have to carry or lay up from a hazard. The GPS is a Bushnell Neo XS watch and the laser is a Leupold GX-2i2.

Buschnell Neo Ghost... yardages to front, middle, back, hazards. Pick your club and go!

RANGEFINDER - Bushnell Tour V4 Jolt. Shoot the flag, love the accuracy and legal for tournament play (no slope). Only other brand I might consider would be the Leupold, but when my friend who has one compares distances with me we do differ in yardage. Mine is more consistent and I feel more accurate. He is always asking me to compare yardage. Make you own conclusions. I feel confident enough not to ask someone else.

I use a Voice Caddie GPS, it may not be as accurate as a laser, but neither am I. I try my best and what happens ,happens. Have fun, that's what it's all about, and hit um straight.

Low tech for me!
Sprinkler heads and yardage markers!

Leupold laser.. Best warranty, period.. Mine was three years old and they sent me a brand new and latest edition. I started out with Garmin got, but as I got better, the laser fit better.

I have a Bushnell Hybrid, It is a few years old now, but has the laser and the GPS. Would highly recommend.

I use an older laser and GPS combo that was made by Bushnell. Sometimes I hit it where the laser can't track the whole so I need the GPS. If i had to pick I would choose laser as I have been burned by a GPS before in a tourney.

I use both i've got a SkyCaddie SGX and also got Bushnell Z6 Jolt. Must say when playing my home course i use my Bushnell more often but do find the SkyCaddie very handy when playing other courses

I have a gamin g6 gps which has been good, but will be getting a laser rangefinder in the next couple of months.I really like the front-middle-back distances that the gps gives me but i'm hoping that the laser will help me improve my approach shots to the green knowing the distance to the pin. Along with some practice also.