Personally I've been very happy with the m-audio oxygen series of midi controller keyboard. Theyre cheap + I've bought two and used and abused them a lot for a few years and they still work great. They're very simple but the engineering is really good, for instance how the plastic casing is designed in such a way as to make it durable.
Also the whole point of a midi-controller is that they never go obsolete, its just a dumb input device for whatever software you care to use, as much responsibility as possible is offloaded to the software. Midi conventions have been enshrined in music software and hardware for decades and this will certainly continue.
The only downside is that you cant just turn one on and start jamming, Youve got to turn on your soundcard + boot up your machine and start your software running which means you miss opportunities to just randomly play come up with stuf. The best thing in that regard is a real instrument like a piano or a guitar which you can just instantly play. A synth needs to be plugged in, turned on + amp turned on.
but then the counterpoint to that is that you can bring your laptop, soundcard + small midi keyboard with you in a bag and can work on music when your on holidays or whatever.

I'm just bitter because I bought into the whole Ableton live APC controller thing. It's a fine controller, but without the general purpose functionality you're talking about. And now they came out with the Push controller, and then Push 2 more recently. A more generic controller is a much better way to go definitely. I still have my old m-audio triggerfinger which looks like hell these days from use.

That said, if I were to buy a new keyboard these days I'd buy a dedicated synth keyboard. You get the benefits of a dedicated synth and can still use it as a controller and still get some money back if you want to change up.

If it has DIN MIDI it's cool. I'd never buy USB only.

Also the Beatstep Pro is every bit as buggy as the Internet has been saying, and the rumors about the quality of their customer support are true. I wouldn't recommend getting one even though the hardware itself is really well thought out and pretty solid for the price (which in 2015 means it's slightly more sturdy than a Casio from 1985 but that's what you get these days unless you pay a lot or build your own). I've actually never had or tried anything from that company that worked right but this one stayed because even buggy it's really useful for what I've been doing lately.

They should just accept that their firmware development is garbage and open source their firmware, because even lone individuals working for fun in their free time are doing better work, but even with access to CNC and 3d printing resources it would be a pretty tall order to DIY a comparable controller for 0. Korg has been heading in the right direction at least.

Inside scoop on the Push 2 is that Ableton reps found out what company was being subcontracted to to manufacture the original Push because somebody forgot to take a shipping label off of a carton about a year ago, and they bypassed the middleman (who are a holding of a venture capital firm that owns about a half dozen formerly respectable companies and has been pumping out some of the most disappointing big-name gear of the last decade under a few well known names, while making most of their profits on things like electric blankets and those shitty USB turntables that cost 3x what they should) to make the Push 2, which is basically the original Push without the cost-cutting limitations forced on them by the aforementioned company when the Push 1 was being developed.

Also the contractor that was hired to fabricate the prototypes of the Push 1 was paid ,000 per unit, which is hilarious.

SOURCE: I know a few disgruntled former employees, including one of them who had climbed pretty high up the middle management chain before he got out. I have a few really serious (like 6 figure settlements and gag orders serious) details about some of the top people but I don't feel comfortable sharing those out of respect for the people who told me. Just imagine the most cartoonish, stereotypical workplace abuse of power scenarios you can (short of American Psycho) and you will probably be pretty close enough to get the idea.

Incidentally, Ableton's trade-in program where you get something like 30% off of a Push 2 when you trade in a Push 1, and the Push 1's are reconditioned and provided to school music programs for free is apparently pretty legit and relatively uncynical for something that's also a way to hook grade school kids into the Live workflow as early as possible and finally cement its place as the Pro Tools of EDM.

Except unlike Pro Tools, which is quite possibly the most backward, limited piece of commercial software I've ever owned (because if you ever do any contract work you have to own that shit and deal with stuff like head engineers who have never heard of offline rendering and don't know that RMS measurements aren't absolute, but I digress), Live is actually pretty cool. Not my thing, but pretty cool.

all you really need is a Rave-O-lution

http://www.vintagesynth.com/misc/rave309.jpg

M Audio made some really good budget stuff before Avid bought them. I still hang on to my beat up, secondhand (maybe third hand, I forget now) Oxygen 8 because I haven't seen a more recent, cheap, portable keyboard controller that's as sturdy or has anywhere near as nice a keybed. Not that I've really been looking hard.

I will outhipster anyone in the forgotten, unpopular, early virtual analog hardware arena. I have a secret weapon.

I'm still using a Yamaha CBX-K1 that I bought in the late '90s. I'm fine with using trackballs and graphics tablets to manipulate the pretend knobs on my pretend synths if it means I don't have to worry about stuff breaking.

I can't remember the last time a piece of older hardware failed on me but software shits the bed CONSTANTLY.

But yeah it doesn't matter what you use. I like hardware because I feel like having one box that does a couple of things well helps me focus, plus if I get sick of it I can almost always sell it for cost (because I'm sure not buying it new, unless it's a kit - and so far the only kit I've made that I've actually looked at secondhand prices for has almost tripled in value since last winter). But hell, a guy I know makes really good stuff on just a Palm Zire.