Microphone suggestions?

I need mic suggestions. I have a couple of projects coming up and am looking for help.

I have a DSLR (Nikon D3300) that I plan on using to record so I'm looking for a mic that I can hookup. Would I need an adapter for it? Also, would it be best to have the mic hooked up to my laptop instead? I do use Adobe Audition a lot more so I'm guessing that it may not be a bad idea but I'm looking for expert advise. For those that have a transmitter, would I be able to put a memory card so that who I'm interviewing, the conversation is saved? Please advise.

You need more than a microphone.

You need to use an external sound recorder like a Zoom H4n and a shotgun, condenser microphone.

The technique is called "dual sound recording". You can use a Directors slate (clapper) to sync the pristine sound from the recorder with the poor sound recorded by the camera.

In post, you sync the two soundtracks and once synced, delete the sound from the camera.

Your Nikon D3300 has a 3.5mm stereo audio input. The internal mic is mono. There's no "single best mic" for an external mic. Choices are:

Mono handheld dynamic.
Mono shotgun condenser.
Stereo condenser.
Mono Wireless lavaliere.

We don't know what your projects will need.

My audio "kit" includes:
* Zoom H5 (per fhotoace's good suggestion).
* Audio Technica AT875R. This mono condenser shotgun mic does not have a battery cavity so phantom power needs to be supplied externally - in my case, the camcorder's XLR connection can provide that - you D3300 can't provide power from the 3.5mm audio connector (like some Canon and Sony dSLRs can with "plug in power") unless you add an XLR adapter (see BeachTek or juicedLink). Be sure the XLR adapter can provide phantom power.
Audio Technica AT8004L mono handheld long neck dynamic mic.
Sennheiser G3 wireless lavaliere system mono - with the optional module that allows a handheld mic to be a wireless handheld mic.
Shure SM58 mono handheld dynamic mic.
Audio Technica BP4025 condenser stereo mic.

Then there mounting options… Camera mount may require a bracket, you may want a boom-pole or a mic stand or something else. You will want to use a shock-mount to isolate the mic from the camera - if you don't use one, the external mic, when camera mounted can record most of the internal mic noise the internal mic records (read the manual about the internal mic recording internal noise…).

If you go the way of a shotgun mic, cutting wind noise down may be needed. There needs to be a dead-air space between the mic element and the wind. A zeppelin or fuzzy (aka "dead cat") will help a lot with that. The included foam windscreen by itself is pretty useless.