That's a toughie. In my opinion, you should play what you enjoy more, because that will mean more consistency and better results down the track.
That being said, one of the things to take into consideration is price. A bansuri is considerably less expensive than an orchestral flute, and you could probably even build one yourself without too much trouble. Also, as far as I am concerned, flutes lacking a solid silver headjoint or, conversely, fully made out of silver are a waste of money (I am no specialist though).
The other thing is the material used. I personally avoid instruments made of wood like the plague, because they crack and do not respond well to certain climates, but if you are not too attached to your instrument, that's hardly a problem. After all, a bansuri is not a clarinet and doesn't cost an arm and a leg. But climate is an issue. If you live somewhere humid or with constant temperature jumps (like Australasia), be prepared to have to adjust your embouchure and airflow and make the tuner your best friend.
Ease of handling might be important to you as well. A bansuri doesn't have any keys or rods you could accidentally bend or any key pads that will gather mould and spit and will eventually have to be replaced. On the other hand, a flute might be easier to transport, as it is usually made out of 3 pieces (headjoint, body and footjoint) that fit into an average backpack or instrument case.
I think glissando is easier (and totally possible) on the Western flute. And this is where I have to mention that Western flutes come in 2 major flavours: open-hole and closed-hole. I find glissando easier on an open-hole Western flute than on a bansuri. The fact that the Western flute has action (the keys and rods mentioned earlier) gives a lot more control over the speed and quality of glissandos. The effect is especially noticeable for glissandos that involve transitions larger than a semitone, which are a pain in the behind for non-chromatic instruments. Another advantage of the Western flute is that you can buy an open-hole one and some rubber plugs to fit into the holes when you are beginning to learn it and don't have the proper finger positioning figured out yet. So an open-hole flute can be transformed into a closed-hole one in a matter of seconds, whereas you will have to be precise about your finger positioning on the bansuri from the get-go.
Non-chromatic instruments (like bansuri or harmonica) can be played chromatically but involve a lot more "cheating" (like bending notes or not fully covering the tone holes). Theoretically, you could get a bansuri in 1 key and learn to play it chromatically, but most harmonica and bansuri players keep a few around anyway.
As for your final question... in all honesty, I think neither instrument is well-suited for a beginner. It took me hours to get my first tone on the flute, and I've heard stories from other players who had spent weeks. So unless you already play another instrument, be ready for a world of pain. Both instruments are very unforgiving and require precise posture and airflow. The mirror will be your best friend along with the tuner.
Dark humour aside, playing music usually comes down to playing music with others. So your choice will be affected by what kind of music you plan on playing. A Western flute is a versatile instrument suitable for classical music, jazz, metal - you name it. And other players will usually have nothing against you joining them. Sadly, a bansuri might not be as welcome.
Even if you only want to play by yourself in the dark ambience of your cellar, acquiring note sheets for bansuri will be a lot more difficult (and will probably involve getting through some non-Western notation as well), whereas you can get virtually anything for flute. The fingering charts for bansuri involve non-Western terminology as well, which you will have to get familiar with.
I hope this gives you a better idea of what to take into consideration. I'd personally get both. If you get the Western flute, stay on the lookout for intermediate models with a solid silver headjoint. A lot of students give up their instruments for relatively cheap once they finish school. And an intermediate/professional instrument will also sell better (and sometimes at a profit), so if you decide you don't like it, you'll be able to get your money back.
