All depends wich direction you want your "collection" to go. If you want a workhorse, then, it's just what you like...
If you want it for collection, then, for the 1640 series, what was originally imported, look for calibers such as .243 Win, 7mm Rem Mag, .308 Win and 7X57. It's a very good starting point. The .270 Win and 30-06 Sprgd are "quite common".
You can try to get a H-5000, a 3000 Crown Grade one late, one early - a 3100 would just be so GREAT! - it's a real "rare" item -, a 4000/4100 any of the "Presentation" or "Imperial" models, correctly stamped as such.... You can try to find Epps creation... some also collect the helstock (fullstock) variations models 456/458...
For European production, you need to have have some in (originally chambered, no rechamberings) in 9.3X62, .358 NM. - the rest of the calibers are "less desireable"....
They had the same basic model lines, with slight differences, and different names.
From there, you can also collect the Dalhberg rifles....
Then, you also need a 46 and a 46A (M/94 in 9.3X57), a 46B (M/94 in 6.5X55) a 146 (a M/98 in 9.3X57), at least one early 640, based on the M/38 (9.3X62 is THE one), one of the early 640 using a M/98 action (8X57 are DIRT CHEAP), one of the "intermediate ones", before the coming of the "H-type" actions, and one late ('49 and later). Then, after you will need another M/98-based rifle, so, you need at least one "1951" or late M/640 and one of the M/1000/1100/2104....
You could also go for any of their single shots rifles - there is plenty of models, the supply just isn't up to the demand.
There are all the 22 and Flobert models, then, you have the double / combination guns and the shotguns....
And 'I'm not talkin' about all the "side productions" Husqvarna ever made...
So, after all, you have the rest of your life to acquire good Husqvarna quality products...