Depends on where you are flying, to me.
Before the Orca buff, used to boost with one and mine with five barges.
in high sec, cause of ganking and lazy pilots or pilots semi afk a lot while reading guides and making isk… maybe porpoise and t1 barges… covetors for example. they are dirt cheap and you will likely get ganked sometime if you are not on your game, don’t use alts in surrounding systems for monitoring local, or don’t use local in the system you are in and never watch d scan…
In low sec or null sec, where it is both safer and can be more dangerous, Id use Orca, and t2 barges. Why? because your time on gird is what is pays you, so while its safe and you are there, you need to get the most you can per minute. so max yield is at least, my intention. and I do this because I am ALWAYS watching local, I mine in 0 local system with a station and access to a JF, AND I use alts in surrounding systems to notify me one system out when someone is coming.
Gives me time to warp my fleet out to the station. 0 local mining, you can use Orca and t2 barges, even in high sec, if you use the same precautions, you may never get ganked mining.
Since the Orca buff I think the Orca is pretty boss, and would maybe reccommend you getting a second Orca capable pilot, at least for flexibility, and USE that char as a t2 barge miner with the one Orca as a booster.
When you get 4-6 accounts, you want a booster and the rest miners, and once you get so much ore its hard to haul, you need another account for a freighter pilot. Mine an hour at a time, fill up 20 cans in the belt site, mtu the cans together, then warp the freighter in to scoop the goods and dock back up and wait for the next hours time.
Your strategy and where you are flying has a great deal of what you should fly and how it should be fit. Though this may be arguable, and unique to the needs of the corp or player, and some fits and tactics may seem illogical to some but for you, has a direct benefit most overlook. Just stick with your style and try to think of counters to threats, best counter to me, is mine in 0 local, lowest sec as possible, with closest trade route available, and use scouts to watch surrounding systems, if you do it right, you will find a pocket and in there a system in a dead end where you can form your scout at the choke point and cloak up on the gate ahead and just alt tab to the miner account. when you hear gate fire, be sure you are looking at the gate, you know to alt tab to the scout and note the ship, ship name, character name, and link in intel, and warp your guys to safety, or at least align out for that fleet warp.
Preparation is key, and I never mined with less than covetors or hulks… if you can afford rorquals and ■■■■, then join an alliance. mine in that. best mining ship in game and you dont need tn accounts to mine like it!