I've had a 159 1.9 JTDM Lusso for almost 8 years from new. It started off as a 150bhp, but has been chipped to a whisker under 200 and has now clocked up 120k miles. Oomph wise, it's fine for everyday use and has been almost fault free for all of those miles. I had a few initial teething troubles when it was new with some electrical gremlins in the central locking and mirrors. Long story, but it took about three months to sort, largely due to being an intermittent fault. Other than that, Boost pressure sensor failed at just over 110k (common fault, so maybe I was lucky) and it had a set of injectors just after. The usual EGR valve issues at about 80k. The other issue that probably won't apply if you're looking at a TI is the swirl valves. The early (alloy) manifolds were prone to swirl valve and linkage failure. The later plastic manifolds have a different design and don't seem to cause issues. I've not had any issues with mine (plastic manifold), but it was badly coked up prior to being removed and cleaned out at 100k ish miles.
They do have a bit of an appetite for front tyres. I usually get about 18-20 out of Conti sport 3s with a mix of normal and spirited driving. They are quite sensitive to geometry and it's well reported that thyres scrub quickly as bushes get worn. Economy wise, expect about 40mpg in normal use (I can get mine into single figures if trying very hard). From what I've read on the Alfa forums, the gearbox on the 1.9s is made of cheese and is a weak point, plus the diesels have a dual mass flywheel which can be prone to failure. Mine's still on the original despite mileage.
I would be looking at a 2.0 rather than 1.9 as like most cars, are better sorted than the earlier ones. The TI is a nice spec (sadly not available when I bought mine). I'm just waiting for the replacement to eventually be available from Alfa. I love mine and it will be missed when sold.
Hope this helps.