If you were to buy a groupset which one?

I want to keep costs to a minimum but I’m worried that 9speed will become obsolete before the kit wears out and I’ll end up paying loads for obscure parts or upgrading again.

Is 105 significantly better in terms of performance.

This is instead of a pompetamine so winter bike maybe used for the occasional bit of touring.

9 speed will I imagine slowly fade out, but probably not in the lifetime of your kit.
I’ve just invested in Tiagra for a high miles training bike and winter use.
Reason being, I also want to keep costs down initialy and some of the running costs will be cheaper i.e cassettes.
105 is sweeter than Tiagra, but really not an issue for general non racing road use.
I run three bikes, two road, one with Ultegra and one with Tiagra. And a crosser that’s still running 2004 105, which is smoother than my nearly new Ultegra.

does the tiagra have STI shifters? or those thumb ones?

if not STI i’d go with 105 personally (and i’d go for 105 anyways (i did))

Tiagra goes 10 speed just about now, with a nice cross and touring friendly 30-12 cassette…

I would go for the 105 10 speed if I could afford the premium over the Tiagra. The hidden cable routing looks much cleaner and the brakes are noticably better. Regularly maintained road kit lasts ages so running costs are not quite as high a factor as they are on an MTB.

What he said
The 5700 105 with concealed cables is very neat and work well. Nicer feel to it than the Tiagra