Very much either really. It does depend on time of year, weather, etc. but it’s not cut and dried. There are advantages to both and it depends what you are comfortable with.
Tarp & bivy.
It’s not a tent and is often seen as less threatening so you can get away with more – it’s not really “camping” to many people.
You aren’t limited to having to find a flat tent sized footprint plus room for guy lines etc, you can be quite inventive in using available features – trees, walls, old buildings.
Can be lighter but depends on what you compare.
Can pack better on bike. I made my own poles from an old tent and cut them so they’d fit in my frame bag, you are stuck with the manufacturer’s idea of what a tent pole section should be.
Easy to adjust according to conditions: tarp edge to floor in windy/cool conditions or raised in warm ones to get a draught.
Tent
Much better if it’s really midgey
Slightly warmer as you’ve an enclosed airspace.
Better if you have to pitch in an exposed location in poor weather.
More familiar to most
I’ve a Terra Nova LaserComp 1 which is 900g or so and can fit two (just) in it. My tarp setups weigh from 300g to 900g including pegs and poles (not including bivy bag, or bags if there are two of us) – if I’m on my own I wouldn’t take the 900g option as it’s just too much space. My bivy bags range from 130g (BorahGear cuben fibre) to 500g (Alpkit Hunka XL). The BorahGear bivy has a bug net and can be completely enclosed so is fine for dealing with midges.
Where you pitch can have a big impact on how anything performs: if it’s going to be midgey then finding somewhere open and in a breeze will deal with them. Conversely if it’s blowing a hoolie then somewhere in the trees is better. Camping by water will tend to be cooler. Etc.,etc.
I’ll be using the Jenn Ride as a final shakedown for the HT550 so will have the lighter stuff listed above.