Andy,
In my opinion the Swedes are not as good as the 'Eastern' figures in the By Fire and Sword range. The style is not my cup of tea and I find them very generic with some odd details like the shape and size of the hats. All of which makes them look "wrong" to me but this is at least partly a matter of taste. IMHO you'll find better 'Swedes' with Essex or Matchlock (see below)
When I built my Polish army I used Essex figures but found the range incomplete due to a lack of command figures, musicians and standardbearers for the cavalry. I was able to improvise officers and standardbearers by mixing figures and using the high command pack as well as making use of troops with lances for the flags. Essex Cossack range supplied unarmoured lancers to mix with the unarmoured horse archers.
Another dislike was that the mix of cavalry types incomplete as well, no unarmoured cavalry with carbines, the only Pancerni with a carbine has a weird pose and so on. No bad figures, easy to paint even for an at best average painter like me but flawed. The "Rajtar" figure is a little gem though as it is an unarmoured western cavalryman with sword who can be be very usefull as a Swede & German.
For Polish figures I would look at other makers such as Old Glory 15s and Polish companies like By Fire and Sword and Qr Miniatures. There is also Legio Heroica which look superb but are really for the 1683 army.
The ECW/Generic Western 17th C figs are more complete and you can find all you need in the way of cavalry, infantry, dragoons and artillery if you prefer to buy everything in one place. There are some flaws though how large they can be precived to be depends on how pick one is. For example the cavalry are usually cast with a carbine as part of their equipment, much of the Swedish cavalry didn't have one and it is an added detail to paint. The range also suffers from Essex use of cast on flags so either you have to care fully remove the existing metal flags or be skilled enough to paint the flags by hand. (For the infantry one can paint up pikemen as ensigns and use paper flags with out any problems). The artillery suffers from lacking good 12-pounders and 3-pound regimental cannon, a real drawback given that those were very popular with the Swedes.
Today I would not rely as heavily as I did on Essex but rather shop around for figures much more.
Matchlock miniatures makes a lot of varied and usefull ECW figures, I like these a lot and drafted a lot of the figures I recived as part of an ECW order into my earlier armies. You can build some very varied cavalry units with what is awailable in their ECW and TYW ranges even if you limit yourself to troops wearing hats only. The major drawback is that the cornet is wearing a typicaly English Montero rather than the wide brimmed hat used by Germans or Swedes most of the time. The infantry is also varied and I particularly like some of the musketers who have a rugged "campaign" look.
Old Glory 15's offers several diffrent packs of 17th Century cavalry in hats as part of their ECW & TYW ranges. (Which can be found under "Renaissance and Samurai 1530-1615" link ) I'm going to use these next to expand my Swedish cavalry. Oddly enough I'm less fond of the infantry and it is more distictly TYW than mid 1650's
Peter Pig makes some very usefull artillery, with 4 diffrent gun size it is far easier to recreate 17th Century artillery than with the Essex line up of two different of huge 24-pounders, a 6-pounder and what looks like a 1-pound gun. If you use them PP also makes casulty figures.
To give you an idea of how the apperance of the troops changed during the period
Paintings from 1610-1620
Paintings from the 1630's
Paintings from late 1640's to early 1650's
