Tyranids excel in close-combat, with Monstrous Creatures, and numbers. So, in contrast, you're going to want a small, elite force that is stronger in firepower. A lack of huge killing machines would also be preferable, I assume.
The ideal force to me would be Daemonhunters. Their basic troops, Grey Knights, are more expensive Space Marines with lots of heavy firepower. As a result, they're very low in numbers and their units also have a lower maximum capacity. Also, they have powerful vehicles too, which provides you with a new experience as well. The closest to having any Monstrous Creatures will probably be the Dreadnought, which is actually a vehicle.
However, the Daemonhunter's Codex is incredibly outdated so it may not be worthwhile, particularly if they're due a new one sometime soon. Rumours suggest they are. Witch Hunters, I believe, are in a similar situation to Daemonhunters. Consequently, you may be best off looking at Space Marines, especially considering they've recently had a new Codex released.
Whilst it may be worth waiting for the new Blood Angels, they're incredibly close-combat orientated, and whilst lots of their more elite units are highly expensive, they wouldn't vary too much from 'Nids in comparison to your standard Marines. Utilising the Codex efficiently, you can create a very forgiving and flexible army, that can either be nicely balanced or totally focussed on one extremity. It's your choice.
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