Hey overload, I'll try to answer your question in a little more detail. 1st to the difference, a reflex sight is usually a red dot, or lit reticle sight, does not have to be a dot. They also can come in different colors. But a dot sight can come in many variations.
1) Reflex has only one lens forward of the diode projecting the image, dot or otherwise. One exception that comes to mind is the trijicon ocluded gun sight and the old weaver quickpoint, you do not look through these, rather keep both eyes open and the dot appears on what your looking at through the ( binden aiming concept ) look that one up. In a reflex sight there is no finite eye relief, one of the plus factors, having no magnification, they can be mounted from 1/2" to as far forward as you can focus, another plus factor, most are very light weight, another plus factor. Some single lens reflex systems are as follows, but definitely not limited to this list.
1) C-more.
2) Eotech or bushnell holo sight.
3) Oki dot
4) Tasco, optima, J point, or doctor optics, all variations of the same sight.
5) Trijicon, reflex and ogs.
6) Hakko
7) tru glo
Google them up and see what you find.
Red dot sights of other kinds usually have a tube, and more options, multiple reticles, multiple colors, magnification, again, no eye relief problems unless you use a magnifier that attaches before the sight. Some of these include but are definitely not limited to this list.
1) Aimpoint.
2) Tasco pdp 2,3,4,5.
3) Trijicon tri power
4) BSA
5) TRU GLO
6) REDFIELD
7) BURRIS

LEUPOLD, GILMORE SIGHT.
GOOGLE these up as well.
I own both. There are pro's and cons to each, just like everything else.
Except for the Trijicon, C-more, and Eotech, the others are fragile, fine for match shooting or even hunting, as long as your aware they don't take impacts very well, recoil yes, dropping them on the sight itself no. Some reflex sights ( c-more) have very crude adjustments that will take time to sight in, and your not going to make field adjustments for elevation. Trijicon and Eotech have click adjustments.
The tube sights usually are more robust, not always. Have better adjustments, changing intensity levels of the dot and battery changes are usually easier.
Now which is better, depends on what your target is and how close, IMHO, reflex sights really shine at close quarters, shooting and moving, kind of like watching tv as you move, your not totally focused on what's in the tube, your more aware of your surroundings. I've shot my Eotech out to 200 yards, and it works, but not for headshots. My 2 C-mores are on handguns, great for 25 yards and in, usable for 50 yards, but beyond that the dot is too big, now you can chose the dot size, mine are 4 minute and 8 minute dots. a A 2 minute dot is available, and I would recommend that for a rifle. The Trijicon is very robust and mil spec. The Eotech is the same, if you get the military model. My Eotech is mounted on a flat top AR, and inside a 100 yards, I like it.

Now to the tube sights, as mentioned previously, generally more robust, lighter than most scopes, more like a normal scope when viewing, some of the less expensive sights will wash out in bright sunlight. I own a tasco pdp 4 mounted on a handgun, ugly but a big field of view and inexpensive, 2 aimpoint cmp 2s, awesome on a rifle, 2 power magnification, 10,000 hour battery life, change batteries on your birthday every year. The newest ones offer 50,000 hour battery life. IMHO, best for rifles, click type adjustments with a screwdriver or knife tip. Multiple reticles, dot, duplex, circle with a dot, 4 different dot sizes with a turn of a knob. Maybe a little bit slower than a reflex, depending on the conditions. Inside the house I give the reflex a big thumbs up, out in the front yard, both are good.
A final observation, on handguns, a reflex sight can be problematic if you don't practice with it, when you bring the pistol up, and you don't see the dot, you have no idea where it went, especially week handed or awkward shooting stances. The tube type naturally center your eye through at least 2 lenses and are easier to recover from.
My 2 pennies.