Am not an expert or collector, so take my comments cautiously....

Best is to have a budget- tell us the range of $$ you willing to pay
There are models between 10-20k, right up to 50k and above...
Then, which case style sings to you? Luminor? Radiomir? Sub case? etc?
Once you have the above resolved, you can then short list to several models. Plenty of old threads here in MWF that you can search.
Many like to start off with base models. 000, 112, 210, 183...Relatively cheaper but very much respected.....
Do bear in mind that Panerai been releasing a `newer version' of these base models... equipped with 8 day movement...pricier of course..
As long as you're not hooked with vintage Pams and have a realistic budget and don't buy blindly, you should be alright....
