There are significant differences between most of the Futura fonts on the market
http://www.myfonts.com/search/fu.... Some simply have different character sets with varying degrees of language support or extras like small caps and oldstyle figures. And some actually differ in letterform design.
As a brief general reference, here are some key design differences between a few of the major releases:
Neufville http://www.myfonts.com/fonts/neu...As the owner of the Bauer foundry assets, Neufville claims to have the most accurate digital rendition of the original Futura drawings. This may be true, but Neufville isn’t necessarily the best font maker in the business — they have some spacing issues (see the ‘ro’ in the Bold above, for example). Still, this release has the largest family of styles, with small caps and italics for nearly every weight and width.
URW http://www.myfonts.com/fonts/urw...Similar in design to the Neufville. Perhaps with better spacing. Not as large a family with all the extra small caps, but it does have some display weights that could be useful on occasion.
URW Futura No. 2 http://www.myfonts.com/fonts/urw...I read somewhere that this variant appears to be optimized for small text. It is wider, the ascenders are shorter, the counters are larger, and the apertures are more open. On the other hand, the round glyphs (a, g, e,) are more true to the circle than the other URW version. This is especially apparent in the 'e' which looks like it was drawn by an engineer with a compass. This attribute doesn’t make this a great text face, but if you want that strict geometry, No. 2 delivers more of that than most of the others. Only 5 weights — no Light, the thin Book weight fills that gap. The Extra Bold is unique and I think puts on the weight more successfully than the other Extra Bolds out there.
ParaType http://www.myfonts.com/fonts/par...This version and E+F’s offer the broadest range of weights with 7. (This is because their Heavy is actually usable.) No small caps, though. ParaType is a Russian foundry specializing in Cyrillic, so if you think you might need Russian someday, this is the one to get. Otherwise similar to URW and E+F.
Elsner+Flake http://www.myfonts.com/fonts/ef/...Virtually the same design as URW and ParaType. A "Heavy New" weight corrects the problems with the original Heavy.
Bitstream http://www.myfonts.com/fonts/bit... This Futura is a major redraw from the original. In many ways it is a more successful typeface because it abandons some of the strict geometry in favor of a more harmonious whole, but it may not be the Futura you were expecting. The acsenders and descenders are shorter, letter widths are more uniform, weights are more consistent (note how little the lettershapes differ between Light and Bold), and the rounds (a, g, b, d, p, q) and 's' are significantly different than other Futuras. In short, this is the least true to the source but may be the most versatile Futura for contemporary design.
Scangraphic http://www.myfonts.com/search/sc... http://www.myfonts.com/fonts/efs...This version is unique in that it offers separate families for display (SH) and text (SB) use. The display version is narrower, very tightly spaced, and has no ink traps. Unfortunately, it’s not truly optimized for use at extra large sizes because it still suffers from overshoot distraction (see
Typefaces and Fonts: Why do the points on Futura in letters like A and N rise slightly above and below the heights of other capital letters?). A versatile 7 weights in each family.
Adobe http://www.myfonts.com/fonts/ado... Avoid this one. Adobe produces some excellent original designs but many of their early revivals (see also Helvetica) are a bit of a mess. In many weights the round shapes are much more oval than circular. In some cases they are even egg-shaped! The Heavy style is a particular atrocity.
Linotype http://www.myfonts.com/fonts/lin... Same design as Adobe’s (I believe it was licensed), though spacing, small details, and character sets may vary.
This overview just touches the surface. There are other design differences (some fonts include the wacky experimental glyphs from Renner’s original drawings), other foundry versions and alternatives (check out the early American competitor Twentieth Century
http://www.fontshop.com/fonts/do... and the very useful East German follower Superla
http://www.myfonts.com/fonts/pri...), and many other non-design considerations, such as language support, figure sets, licensing costs, and webfont availability and quality. I’d love to do a proper review if someone wants to fund it.
Update (Oct, 13 2012): Added URW Futura No. 2.