>>317816
From what I've heard you choose one of the 'good' armies. Also one of the most flexible. You can play as swarm, balanced, elite, what have you. The only downside for Tyranids is that monstrous creatures suck compared to vehicles, and that's what you get instead of vehicles.

Consider looking for a starter army on eBay. You can save loads that way.

I don't play Tyranids myself, but it seems to be a difficult yet fun army to play. The lack of vehicles and troop special weapons is something you will probably curse. Termagaunts with Devourer guns can be incredibly lethal. Lictors can turn battles, but depends on getting that deep strike roll right. Genestealers are good on paper, but enemies tend to focus fire on them because they're such a pure offensive unit. A lot of tyranids will lose melee battles in surprising circumstances. Especially when assaulting things that use terrain cover as their initiative is suddenly down to 1 - unless they count as having offensive grenades, which I remember as being rather rare.

find some Carnifexes or Trygons for cheap on eBay or something. You will basically be required to convert them into Tervigons, they're pretty much a must have unit and don't have an official model. They're a Toughness 6, Wound 6 3+ save monstrous creature that can be taken as a Troop slot (scoring unit) and can produce 3D6 FREE Termigants every turn until a double is rolled. They can also be fielded as HQs. I pretty much never field my Nids anymore without two of them in my Troop slots