For individual infantry figures, I would recommend either:
Category 1: Robust
Older H&R
More robust, but less detailed. Not abnormally sized or shaped. Great selection of poses in the packs, and easy to buy separately to get the mix you want. Sturdy figures that look reasonable enough when painted up well, and stand up very well to game day use.
Category 2: Better details
GHQ Individual Infantry and Individual Heavy weapons
Really beautiful miniatures, with exceptional detail even at such a small scale. Not fragile (as with some other vendors), but they will require a bit more care in handling than the Category 1 figures above. The poses and the variety in the packs are not always the best for building actual 1-to-1 units. But if you are abstracting your figure scale to almost any 1-to-many rate, where you are not counting the actual ratio of riflemen to LMGs to small mortars to medium mortars, etc., then you will be just fine. More pricey than your other options, but this scale is still WAY less expensive than larger scales.
Newer H&R
I have just recently received my first order of the newer H&R figures. They are on my workbench now, and I am quite impressed. These are the first figures I've seen that I would consider to be in direct competition with GHQ Individual Infantry. Excellent details, well proportioned, apperently reasonably robust, and as with older H&R they come in useful combinations of poses and are easy to buy either in packs or piecemeal. I'm only supplementing an existing GHQ-based force right now, but I will be looking in the future for opportunities to build some new force primarily with these figures. Less expensive than GHQ, particularly if you don't have to buy twice as many mortars and HMGs than you'll ever need, just to get the quantity of LMGs you want.
Others I have tried in the past:
Adler
I have a lot of respect for the Adler line. I know many gamers who love the figures. The poses and the detailing are excellent. I have seen some complaints that they are not robust, but I have not experienced any problems in the cases where I have gamed with other players' Adler figures. The exaggerated proportions just don't do it for me, in particular the large heads, so I don't have many in my force. That said, they do look good when painted up well, and Adler does some great poses and bases (the gun crew bases are real gems in terms of how they are set up). The variety, packs, and ease of getting the pieces you want are all top stuff. So kudos to the line, they are worth looking into, but alas they are not on my favorites list.
Scotia
Inconsistent from one set of figures to the next. Some look very nice, but with some I honestly can't even tell if they are WW2 soldiers or sci-fi space alien robots. I freely mix GHQ and H&R old or new, but several of the Scotia figures that I've bought were rather too large to work with my other 6mm figures. All of that said, some useful poses, and if you aren't too stressed about 8 foot tall soldiers, maybe they'll work for you. I do advise starting with sample quantities before going in with a large order.
(ex) PFC C-in-C (now) LegionsIVHire
The C-in-C line was recently turned over to LegionsIVHire. The crisp clean castings of C-in-C always put their miniatures at the top of the list for visual quality. But the infantry was always a bit of a poor cousin to the tanks and planes. Not enough poses, some really awkward poses, and figures that were just too fragile for game day needs. For many years my WW2 US Army infantry force was based on C-in-C figures. I don't think I have ever taken them out of their storage without having to chase down and super-glue back into place some figures broken off at the ankles. I recently replaced them with older H&R. I still have a quantity in my "extras" bin, and they often serve as head-and-shoulders for tank COs or splayed bodies for casualty markers. But I haven't bought any for use as infantry for a long time.
Just my observations. Your bootage may vary.
-Mark
(aka: Mk 1)