WHATS THE BEST OPTIONS CREATING RYTHYM GUITAR TRACKS 

Gerald,
I do not have a "best option".  For midi, input can be via piano roll view, staff view, or keyboard which ever your most comfortable.  I create the chords the hard way but it makes the midi sound more realistic to me.  First get your strumming pattern down exactly how you would actually strum the part.  Then you insert the rest of the chord for each beat.  Remember here that as you strum, you really only play about 3 to 4 strings of either the up stroke or down stroke.  Down stroke you usually play the lower strings, and upstroke usually the higher strings.  Duplicate what you actually do.  Don't just copy and paste (not yet).   Once you get the strumming pattern and the actual strings played for each chord progression, then you can copy and paste in the rest of the song. For a slow strum, I play with the timing of tics between the notes of the chord, so each note is played at a slightly different time. To create the sound, I usually make two tracks and I will use different guitar patches in each track, or I might play the same chords a little higher on the fret to give acoustic guitar more chorus.  Then there are all the effects available.  Also, record the chord diagram actually used in each bar, we all forget things as time passes.

thanks

There are now about 4 or 5 great guitar libraries that include strum engines.
 
Most require Kontakt 5 or greater, but one company, Virtual Guitarist, has four products that could cover all your needs. Iron, Amber, Sparkle and Silk. And they offer a free 30 day full featured demo of all four products.
 
Buying all four products at once saves you 35%, but that does come at a hefty price.
 
 

This is a very inexpensive (but good) acoustic: StrumMaker_IV by Indiginus
 
Also checkout http://www.amplesound.net/en/index.asp: they have everything from guitars to bass's and the included Riffer software is very good/useful. 

The "best" way? Depends. On the style, genre, type of guitar. Sometimes a chord sequencer is the way to go - it's convenient, fast and requires almost no skill. MIDI chord generators are another option. Or you can play the chords on a keyboard, which takes a lot of practice. Or you can plunk in MIDI notes in the PRV and use a guitar library with pre-sampled strums.
 
That's because this is a two-part question: first, how to create a convincing strum, and second, how to string strums together in a convincing strum sequence.
 
First of all, a big +1 for SM4. Includes both 6- and 12-string guitars and ten body IRs and an easy-to-use sequencer. You can create up to 12 strum patterns and switch between them with keyswitches. A useful instrument and a real bargain at $46 (!).
 
That said, SM4 is really best for tracks where you just want an acoustic guitar to fill in the cracks, rather than something up-front, e.g. the only instrument track in a singer-songwriter type composition.
 
Most of my sampled rhythm guitar tracks are played on a keyboard. Once you get the hang of that, you can use any sampled guitar instrument.
 
Another good one, but considerably more expensive ($179), is Orange Tree Samples' Evolution Steel Strings. All OTS guitars have a strum mode and a flexible strum sequencer.
 
All of the above is based on the assumption that you're talking about acoustic guitar rhythms. For electric guitar, there are GOBS of options. Check out Indiginus' Renegade, a favorite of mine for both rhythm and lead. And of course, OTS has a bunch of suitable offerings as well. I'm especially enjoying OTS' Rickenbacker 12-string.
 
If you're specifically into heavy genres like one of the many flavors of metal, then that opens up a whole 'nother set of possibilities. However, those genres don't lend themselves to sequenced chording like acoustics do. For chugging power chords, I tend to hand-plant those in the PRV. In those genres, you might as well go for a product that's specifically targeted at that market, such as Shreddage from Impact Soundworks.