Step1
Here is a rundown :
Frame marquees: clearspan structures with no central poles. These have lowish roofs and are very practical. Some of the advantages of frame tents include:
Frame marquees need no space around them so they can make use of every available inch of spaces if space is at a premium. They can also butt right up to a building
The absence of poles inside means an unobstructed view for speeches
They don't absolutely need to be pegged into the ground so can be put up on hard surfaces and weighted down. This is not a good idea in winter if strong winds are expected though.
They can be joined together in L or U shapes for example. So frame tents work well if you want to fit a marquee into an awkward space.
Step2
Pole tents: more traditional with... well, poles. Better suited for fairytale weddings or classic styled events if that is what you want (though these style can also be replicated in frame tents if the practical advantages weigh heavy). There are different types of pole tents:
Tension tents with high sculpted roofs. Dramatic. Good if you want to really impress.
Plain pole tents. Less striking, more affordable, pretty.
Big tops - large, round, with a high central pole, as used for circuses. These are fun, but are not widely available.
Step3
Ethnic tents: increasing popular, typically for more unconventional events. Usually decorated in the appropriate ethnic style or in bright colours. They include:
Mongolian yurts - sturdy structures with a homely atmosphere
Indian mandaps - highly decorative with elaborate hanging flaps and often printed linings. Typically, decorated in Eastern style with lots of lights, metal lanterns etc
Tipis - native American and Scandanavian styles available. For very unconventional parties.
Step4
All these marquees come in a range of sizes. For larger events, you may be limited to the more widely available frame marquees and traditional style tents. Few yurts and tipis will seat more than 100, though you may be lucky and find a local supplier.
In practice, you will be limited by the options available locally so you will have to look around and see what you can find. Ethnic tents, in particular, may be difficult to source away from major population centers.