Edelbrock vs Holly Carburator?
Actually in an old Hot Rod magazine they once did a comparison. They were rather suprised that a stock Autolite 4100 actually outperformed a Holley 600 and an Edelbrock in informal testing. The 4100 was one of Ford's better designs. Pony Carburetors is a company that specializes in rebuilding and restoring old carburetors. They hold VERY high opinions of the 4100. You may already have the carb you're wanting, it's just showing its age and in need of maintenance.
I have a 4100 on my wife's car. Basically because I had one laying around when I needed it. We like it just fine. She says it gets better mileage than the stock Ford/Holley it replaced. No real numbers though. It does seem very responsive to me and definitely fun to drive.
I have an Edelbrock on my rather modified Ford truck. It does the job and is quite reliable. The truck is seldom driven lately but is ready to go whenever. Edelbrocks are better about being left to sit for long periods than Holleys and need much less attention in general. I like to use my truck, not fiddle with it. It's just an old truck really, not much too look at and got a few problems. But being slow is NOT one of the problems. : )
I have a Holley on my very modified Mustang. Basically because the Holley is highly tunable and is a better match to what other stuff I've done to the car. I don't need my Mustang to drive every day, it's a weekend car. I take pleasure with fiddling with it. Holleys respond very well to regular attention. Mostly.
So as an owner of all three, I'll boil it down.
4100's are hard to find. When you find one it'll be pretty darn old, Ford quit making them a long time ago. And as such, you shouldn't expect much out of it until it has been rebuilt to optimal condition. But in good shape, one is very hard to beat on a stock to mild 289/302/5.0. The "small" 4100's are rated at 480cfm, pretty much an ideal match for a mild Ford small block.
A bit cheaper and easier to deal with is an Edelbrock. If nothing else, they are very reliable. Many folks just bolt one on and go with no trouble. You can tune them to your needs though. An Edelbrock 500cfm is pretty close to ideal for a mildly modified 289/302 engine. If you plan on doing a LOT more engine upgrades, you might want a 600cfm version.
If you don't mind tuning one regularly and want all-out performance a Holley is about the best way to go. The usual Holley starts at 600cfm, really too big for a stock engine. I understand the "Street Avenger" series come smaller. One of those would likely be a better choice. Folks that run 600cfm Holleys often are found complaing about the carbs being difficult to tune to their engines. "Stumbling" upon take off is a VERY common complaint and not always easy to fix.
There are many Ford and Mustang forums out there. I suggest browsing a few and seeing what other folks have had luck with. I believe you'll find a lot of folks have had about the same experiences as me. There are folks that will swear a particular carb is the "be all end all" and all others stink. I tend to ignore those types myself. Which one will best suit you and your car is up to you.