Do not get the GT-10 unless you have spent plenty of time with it and are in absolute love with it. The GT-10 has a flawed pre-amp section that creates a sort of cocked wah sound(look it up on google). It will limit the useful sounds out of it and is somewhat useless for distortion sounds. It does have a lot of nice features but unless you only play clean it will be almost useless for you(you can get around it but why go through the trouble?). For heaven's sake don't buy a pedal until you have spent plenty of time checking them all out with a good amp.
The G-Force/G-Major is a very nice effects unit(very high quality) but AFAIK rack only. They have some newer stuff out like the Axe-FX which I'm not that impressed with but for the versatility is very nice(distortions are good but not better than a quality tube amp). For 1500 it's probably not worth it over a good amp but probably has all the effects you could ever dream of(so it coupled with a good distortion amp would be awesome).
If I were you I would get individual pedals unless you never plan on doing anything more than your bedroom. That or save up for the nicer units(Axe-FX or G-Force or whatever else is out there). The pedals generally sound good and allow you to mix and match. Your not stuck with a pedal that you don't use. It can be more of a hassle though and for simplicity the multi-fx pedals are generally the way to go.
In any case spend a lot of time with them because they generally are not as good as the demo's you see or require a lot of tweaking to get good sounds. This isn't always the case but the GT line has some serious issues. You might love the GT-10 but I can't stand the cocked wah sound.
Most of the effects on these pedals are all the same. They are simple mathematical algorithms that are almost identical for all the units(even the most expensive ones). Generally it is the features that make an effect useful. Having said that, the GT has a nice harmonizer that tracks well and some other effects that work as expected(octaver, chorus, etc..).
What you are looking for is the quality of the clean sound(does it sound too thin or dead) and the distortion. If these suck no amount of fx will make them better(ok, not 100% true but true 99% of the time).
If you're not playing live then get a cheap multi-fx pedal that you like. If you are or will be then save your money for the more expensive quality brands. If you use your computer a lot and are playing near one a lot then you can get a computer based one such as guitar rig which offer just as much if not better sounds than most. I think you can get a free demo for these.
Best advice I can give you is for you to take your time and explore all your options. If you impulse buy you'll most likely be completely unhappy with your choice.