As others have already noted, even small-leaved Nepenthes like glabrata can get "large", that is, many yards/meters long. Having said that, a 6-foot / 2m gracilis is much more manageable than a 6-foot / 2m bicalcarata, even if the gracilis has multiple vines. Leaf size is an important factor in the volume of space your plant will occupy. For small spaces, your best bet is a small-leaved plant that also basals easily. With a constant supply of basals, you can remove longer vines that no longer fit your space. Judging from photos (not personal experience), mikei is a highlander with small leaves that seems to basal frequently. Gracilis is a good lowland example. Ventricosa is also a good bet, as is "thorelii" x alata Kondo (a Bruce Bednar hybrid).
Pot size can also be used to control plant size. Consider, for instance, how large tree species are dwarfed through bonsai techniques. A few Nepenthes growers have kept plants small through using small pots, but this appears to be an under-explored area of Nepenthes growing. But pot size is not the only factor -- choice of medium also makes a big difference. I have several seedlings of the same grex ((smilessi x maxima) x (boschiana x (spectabilis x veitchii))), all in 3.5" square pots, and all growing in 100% inorganic media (perlite or rockwool). Generally speaking, those in pure perlite are far smaller than those growing in rockwool cubes, even though the plants are in the same size pots and are the same age. This is probably because rockwool holds moisture better than the perlite. The perlite-grown plants still look healthy, pitcher well, and don't show salt burn (I water them daily) -- they're just smaller and haven't shown the great leaps in size of their siblings grown in rockwool cubes. Whether they can be maintained at small size in that medium for several years is yet to be determined, however. I'll have to get back to you in a few years.