Last year I wanted to replace my Series 2 with the Series 5 in Titanium, but this model was not available in any nearby Apple store and I could not choose pickup in the store when ordering it online. At some point I decided, that my Series 2 was still fine...
This year the Series 2 will not get the update to WatchOS 7 und I am really looking forward to a watch with cellular option, so that I can leave my phone more often at home. If a titanium model is not available at the store I will probably take the stainless steel watch.
The issue with finding the titanium model in stores, is due to only certain Apple stores are designated stock the titanium model. For example, only one of the three stores in my region will stock the titanium model, mainly because it has the highest amount of foot traffic and it’s One of Apples larger store . So it really depends on your region, but your best option if you want the titanium model, is to pre-order.