Can you please rephrase you question?

It depends on what you are trying to do. If you are looking for mutations then DNA is easier and more stable to work with for small genes but as Tanino says we need more information to be able to answer

Do you want to isolate gene with or without an intron?

With intron

Quiagen DnEasy Plant Mini kit works well, just choose primers that will include your intron of interest during PCR

I would also try Qiagen first. But depending on plant and tissue some secondary metabolites might cause problems, Then you have to use Trizol or CTAB based extraction methods.

Cheers

Agreed with everyone, try QIAgen first. To optimize input try different amounts of input material, I found that with some plants putting the recommended amount is too little and doesn't yield a lot of DNA/RNA, and in some it's too much. Generally for plants, I don't worry about putting too much, the QIAshredder column usually takes care of excess debris/tissue. For RNA extraction, don't forget to properly fix your tissue, eg. in liquid nitrogen, before storing it if you want to for long term storage (in RNAlater or similar). For homogenization many people recommend grinding the tissue in liquid nitrogen; I find it time consuming so I use steel tubes with 6-10 steel beads in each, with a rubber cap, and using a mini bead beater for 10 sec - 3 min (depending on tissue), so if you have that available it works pretty well. Also, for RNA, if you find that buffer RLT significantly thickens with the sample upon addition, use buffer RLC; I tend to use RLC all the time. If you can, also use RNAse A (for DNA extrcations) and DNase (for RNA extractions) digestion, as it leaves you with a much cleaner sample in the end. Good luck!