Some permutation of this question comes up every so often (or very often depending on who you ask). My answer to this question is usually the same, you have two options (in my opinion) in front of you. At a budget of $900-1200, you can EASILY procure two well-made (100-120s wool, full canvass construction, etc.) OTR (off the rack) suits if you have the patience and diligence to do so. You could also get a very nice MTM suit for around that price. Which one you want depends on you. If you have a relatively easy to fit body type, then MTM does not grant you as much of a benefit. It is also important to note that a good tailor can really do wonders with an OTR suit. If you go the OTR route, you can get top-tier brands with excellent craftsmanship (i.e. Oxxford), but your fit will suffer some. If you go MTM, you will still get a nice, very serviceable suit, but you will be paying more per suit for the benefit of a better fit. Now, a word of caution, I can not tell you how many people have gone "MTM" and uploaded photos about their "first fit" and received less than favorable reviews. MTM is really an already existing pattern that has been altered to fit your body better. In most ways, a tailor can do the same thing given adequate material. If you can find an OTR suit that fits you well in the shoulders and chest, there is not much else the tailor cannot fix. That said, the place MTM really shines is in regards to arm holes, in that they can be cut exactly where you need them to be. A higher armhole suit will be more comfortable and allow you to be more "mobile". You can also look for OTR suits that have a higher armhole, such as the Zegna Milano or BB fitzgerald.
Should you choose MTM:
As this is your "first real suit", I recommend using an in-person tailor versus an online one. If you attend a trunk show, you can get a Samuelsohn MTM suit for around $1000-1200 in a decent fabric. You can pick whichever intricacies you want. I recommend sticking with a 2-button, notch label suit, with either flat front or pleats depending on your body type. Navy, Grey, or Charcoal solid colors are all great. Try and select a super 100-120's wool.
Should you choose OTR:
First, measure yourself. Shoulders, chest, sleeves, and total length are the key ones. This may seem kind of awkward, but you only have to do it once. Use these and go to a department store that sells suits and bring a measuring tape. Find the ballpark size (such as 40R, 42L, etc.) that fits you best and measure it. Shoulders, chest, sleeves, and total length are again what you want. The reason I suggest this is that not every brand cuts their suits the same. For example, I can wear a 42L/44L or XL depending on which brand the suit is. Some run fuller in the chest (Oxxford) and some run shorter (Isaia, Canali) as a general rule. Go on Ebay and look at the following brands: Isaia, Kiton, Brioni, Oxxford, Paul Stuart, Samuelsohn, Zegna, Hickey Freeman, Canali, Pal Zileri, Corneliani, Caruso to name some. You can find more by searching these forums. You can buy new or used (just remember to dry clean), whichever you prefer, but the prices I believe you will find are much better. Sometimes similar prices can be found on big sale days at places like Saks. Have patience and buy two suits you like and take them to a tailor. Do not be afraid to ask sellers questions such as, how much material is available to lengthen sleeves, etc. Now, sellers will most often not know terms like "full canvas" or "soft shoulder", but they can always look at the tag and tell you the model of the suit. For example, Oxxford "Gibbons". Once you know the model of the suit, search the forums and the interwebs and you can almost always find everything you might want to know about the suit.
I personally got myself a nearly perfectly tailored Oxxford suit this way for ~400 including all tailoring. My only complaint with it is that the arm holes could be a little higher.
Choose whichever you like and best of luck.