Head to head then. As usual, I pick out winning categories in green, for interest sake - though don't take these too seriously. And note that many categories simply don't HAVE a winner, either because the differences are subjective or because two or more are roughly equal overall:
[If this table is too wide for your phone browser, please try in landscape mode or - better - viewing it on a tablet or laptop? Sorry, but this sort of content just has to be in a table!]
|Microsoft Lumia 640 LTE||Vodafone Smart Ultra 6||Microsoft Lumia 640 XL|
|Date launched||April 2015||Summer 2015||April 2015|
|Best price as at August 2015||£110 on pay as you go, in the UK, various networks||£125, locked to Vodafone, allow up to £10 to unlock to other networks?||£170 SIM-free, couldn't find a pay-as-you-go deal|
|Form factor, weight||Touchscreen candybar, form factor 'just perfect', matt plastic, replaceable backs, 145g||Touchscreen candybar, unremarkable plastic, sealed, 159g
||Touchscreen candybar, matt plastic, replaceable backs, 171g|
|Windows Phone 8.1 Update 2, virtual controls||Stock Android 5.0.2 plus a handful of (uninstallable) Vodafone widgets and applications, backlit capacitive controls||Windows Phone 8.1 Update 2, virtual controls|
|Display||5" LCD with ClearBlack Display 'lite' linear polariser, 720p resolution, pretty good in sunlight when viewed head-on, contrast fades quickly away at other angles||5.5" LCD, 1080p resolution, visibility surprisingly good outdoors in the sun if brightness is set to maximum||5.7" LCD with full ClearBlack Display circular polarisers, 720p resolution, pretty good in sunlight from most angles (see the group photo at the bottom of this feature)
|Connectivity||Up to LTE, Bluetooth 4, NFC||Up to LTE, Bluetooth 4, NFC||Up to LTE, Bluetooth 4, NFC
|1.2GHz Quad core Snapdragon 400, 1GB RAM, nippy most of the time||Snapdragon 615 chipset, 2GB RAM, pretty fast at all times||1.2GHz Quad core Snapdragon 400, 1GB RAM, nippy most of the time
|Web browsing (benchmark: Full New York Times desktop web site, home page)||
17 seconds to fully render (minus ad banners). Internet Explorer is standards compliant, but not as efficient as Chrome on Android. Still, the new Edge Browser is just around the corner, eh?
12 seconds to fully render, on this faster chip and greater RAM. Chrome is modern and has the advantage of syncing with Chrome on your desktop/laptop, etc.
|17 seconds again. Edge will be faster later this year|
|Capacity||8GB plus microSD up to 128GB||16GB plus microSD up to 64GB||8GB plus microSD up to 128GB
|Rear imaging||Good 8MP camera with Lumia Camera 5 Rich Capture options, 1080p video capture||Goodish 13MP camera in good light, pretty terrible in low light, with or without the LED flash. 1080p video capture.||Excellent 13MP camera with Lumia Camera 5 Rich Capture options, 1080p video capture|
|Front imaging||1MP, fixed focus||5MP, fixed focus, OK quality, some colour issues, some extras, including face detection||5MP, fixed focus, good quality|
|Music and Multimedia||Very decent mono speaker, 3.5mm headphones||Loud-ish mono speaker, but poor tone/EQ, typical of ZTE, the ODM here||Very decent mono speaker, 3.5mm headphones
|Gaming||Some decent games for Windows Phone 8.1 but it's a somewhat bare cupboard for the top titles when compared to Android and iOS||A bigger games catalog to choose from, all coming to life more on the higher resolution screen||As with the 640, content exists, but it's a somewhat bare cupboard if you're being picky about specific titles
|Navigation||The HERE Maps/Drive suite is arguably unrivalled in terms of what's supplied out of the box, with the offline routing and maps. Plus good public transport advice and innovative 'live sight' functions.||Google Navigation is very comprehensive, but aside from limited caching of modest areas, struggles mightily when out of data coverage. Live traffic support is good though, and HERE Maps is now available for knowledgable users who seek it out, so there's the best of all worlds?||As with the smaller 640, the HERE Maps/Drive suite is arguably unrivalled, though being transitioned to Microsoft's own Maps code later this year as part of Windows 10 Mobile...|
|Battery, life||Replaceable 2500mAh battery, up to two days average use on a charge||Sealed 3000mAh battery, up to two days of average use, if you're careful||Replaceable 3000mAh battery, two days average use per charge
|Applications and ecosystem||Windows Phone now has just about every mainstream app and service covered, but niche/boutique apps are an issue if you're being picky. Also anything to do with Google services!||Android's Play Store is very fully stocked, second only to the iPhone Store for depth. Everything mainstream is here, plus some boutique/niche apps.||Windows Phone now has just about every mainstream app and service covered, but niche/boutique apps are an issue if you're being picky. Also anything to do with Google services!|
|Upgrades and future||Windows 10 Mobile is scheduled to arrive as an update in October/November 2015||Android updates are always a lottery, but at least this is on the 5.0 branch from the start and many companies are starting to update more in the light of security scares. So optimistic for some updates.||Windows 10 Mobile is scheduled to arrive as an update in October/November 2015, though operation on a 720p 5.7" screen is going to be.... interesting!
Adding up the 'green' panels gives an idea of the sort of competition that these Lumia 'budget flagships' are under: 7 wins to the Smart Ultra 6, 4 to the 640 XL, and 2 to the humbler 640. Given the price differences, the win for the Smart Ultra 6 is all the more remarkable (not least because this is AAWP - though my features are always objective in these comparisons!) and shows what can be done for not much more than £100 these days. Set against the context of flagships costing £600 or so, the Smart Ultra 6 (and similar from other networks and manufacturers - the EE Harrier springs to mind) is all the more remarkable in terms of value.
Of course, it's not just all about money, plus the ZTE-made Smart Ultra 6 has at least one Achilles heel - its camera is demonstrably weak in anything but good light, whereas the 640 XL, for a little more cash, produces images that are often comparable to those from the more expensive PureView devices, and in almost all light conditions. The 640's (and 640 XL's) speaker is also far superior - though the 720p screens on the Microsoft pair pale next to the crispness of the Smart Ultra 6. In short, it depends where your priorities are when choosing a phone.
What can Microsoft do about these new challengers? Well, 1080p screens would be a good start for the upcoming (rumoured) Lumia 650 and 650 XL. Plus Windows 10 Mobile under the hood, of course, which will make good use of all those extra pixels.