That's not an either or question/answer.
First of all, I agree with Padraig. You can get better for less in a 1911 platform outside of Colt. But I would encourage you to begin another thread to see what MO members prefer for a 1911 that's within your budget and then decide among those other answers.
I own several 1911's that I am very happy with, and none of them is a Colt. Two are Springfield Armory, one was heavily customized by a custom smith in the 1990's, and the other is an EMP in 9mm. I also own a target intended build on a Caspian frame, and a S&W M&P 45 asp compact. I shoot and enjoy them all.
As to whether you go with 9mm or 45acp, that's another topic.
How much do you shoot now? How much do you plan to shoot your 1911?
What do you intend to use it for? Paper punching, target, carry, professional security, etc.?
Have you shot enough 45 acp that are you ok with the difference in recoil? If not, I realize that you will need one to accustom yourself to 45acp if you wish to go that route. But if you can borrow of rent one to use for 500 rounds or so, that should give you a taste for it. Ammo will cost you at least twice as much in 45 acp than in 9mm. Will cost limit your ability to practice? Do you plan to modify your 1911 or customize it? The options are nearly endless.
If you intend to carry concealed, do you have a plan or experience for concealing a handgun the size of a 1911? In my opinion, a handgun of this size and weight is best carried "open" in a secure holster rather than concealed unless you are a large individual, or provide security professionally, or have increased need for defensive protection. Others' opinions may vary from mine.
I still shoot and enjoy my 45 acp's, but as I got older--older 50's, I switched to carrying high capacity 9mm's for ease of concealment and decreased weight and reduced fatigue. If you're younger and fit, a 1911 may suit you just fine.
If you want at least one 1911 platform for your own, and don't intend it for defensive use outside your home or vehicle, go for the 45. That's the round it was designed for. There are plenty of good, reliable, and defense tested full sized 9mm handguns that load more than twice the capacity of a 1911 in 9mm, if you feel you need that. Nothing else shoots like a 45.
The 1911's in 9mm are great. Ideal for shooting competitions, fast shooting, and fast reloads--when they are designed or modified for that. They are hefty enough to minimize recoil and stay very near your line of sight for fast follow ups. I think of a 1911 in 9mm as filling a certain niche, rather than being an optional caliber for that platform. Even in 9mm, a 1911 wouldn't be my personal choice for CCW. But it would serve well. I just think there are better options, at least for me.
And I also realize that the elite warriors--Seals, SWAT, Hostage Rescue--preferentially use 1911's as their primary side arm. These guys practice a LOT. They throw more rounds down range in a week than most guys shoot in a year. They also have their own armorers to maintain, modify, and repair those 1911's. Their training is such that reloads and malfunction clears are effortless and automatic. They know exactly where to reach for that second mag, and even the tenth one. They are gifted and talented marksmen. Few of us will ever get to that level of proficiency. It takes motivation, training, and years of practice. I couldn't even afford to buy the ammo to train for that. And with my level of coordination, I'd never get there.
I don't say this to talk you into or out of any decision. I write this in appreciation and awe of what these elite warriors are able to do. They are on a whole different level for the rest of us.
Again, consider starting another thread for MO members' specific 1911 suggestions. You don't need a big budget to get a good 1911.
Good luck in making your decision. Let us know what you decide.