I have my favorites but with present company their is lots of personal taste that comes into play.
I have a 15mm SAGA project that has been in the works for the last 18 months that has prompted me to buy a number of different manufacturers in hopes of getting a force with all unique miniatures.
I have purchased Splintered Light, Khurasan, Baueda, Old Glory 15's, Peter Pig, and a couple from 15mm.uk.
Splintered Light: Very Nice figures with clean crisp casting and good detail, many poses. Probably the largest of the bunch. Not ill proportioned at all but robust ala Battlefronts Flames of War figures. David is first class, can't go wrong. The early Saxons will add some poses for raiders styled forces and the Late Saxons can bulk out a Dane force.
Khurasan: Very nice figures, probably the most realistically proportioned figures. A bit more slight than SL but looks quite good next to them. The Jarl is puny, avoid him. Good casts and detailed sculpts. It may take a while to get your figures.
OG15: The unarmored guys are not as nice as the above. The armored guys seem to have more potential. The casts are marginal. Probably the cheapest but you are definitely getting what you pay for. It's hit or miss with them IMO. I love their Hoplites but the Vikings are a bit lacking. If there is no pictures on the website I think that is a good indication of things to avoid. Armored guys ok, unarmored wanting.
Baueda: I am not a fan of these guys at all. Some like their blocky robust look and I thought they had potential but I was disappointed. They are smallish and weakly detailed. Decent painting on their web presentation make them look better than they are. They would probably mix well with the Sgt. Major stuff or those guys from Poland but for me not to my taste.
Peter Pig: A completely different animal. I would not mix them with any others. Smallish (possibly the smallest, or is it true 15mm?) and detail difficult to discern. The chain mail is sculpted very tiny and doesn't match at all with other lines. That is probably the most correct at this scale but it just doesn't approximate the look well enough IMO. The resin longship I bought is outstanding.
UK15: Tired old line. Avoid. Not worth bothering with for US customers in comparison to other US offerings. Their consistency is too wild for me. I liked a couple Norman Cav I got but everything else except the female adventurers was a big disappointment. Their fantasy stuff is not really 15mm. It's 18mm. I did not get very many vikings and thankfully so.
These are all opinions based on putting my money where my mouth is and ponying up to put them in my hand.
I would like to try out the Donnington New Era stuff but I am a a little unsure. If their were some good painted examples about I'd make a stab.
This topic has come up from time to time, here once: TMP link
Splintered Light>Khurasan>Peter Pig>OG15>Baueda>UK15
BTW, why do you ask?
gets medieval.
