I'm not sure if i should write it as an eight note tied to a dotted eight note, or maybe a half note tied to a 16th note or what I don't know.
First, 5 eighth notes is not either of the values you mentioned in your question as pointed out in comments. There are several different combinations possible to get a note that is 5 eighth notes in duration. A half tied to an eighth and a dotted quarter tied to a quarter are the most common and logical.
The other issue is 6/4 time. In 6/4 time you want beat 4 (the middle of the bar) to be visible since 6/4 implies 2 groups of 3 quarter notes. This will determine the note values used for a note of that length.
Here are examples of notes on and off various beats that are 5 eighth notes long in 6/4 time. For simplicity I used all quarter rests instead of half and dotted half rests:
Examples 1-4 start on Beats 1-4 respectively. Note that example 3 has a quarter tied to a dotted quarter to show beat 4.
Examples 5-8 start on 1&, 2&, 3&, and 4& in that order. Also note that example 6 has a dotted quarter tied to a quarter to show beat 4.